Additional info: I have disabled any effect in Waves MaxxAudio (which is preinstalled on this system)

I have deinstalled and reinstalled the Realtek drivers (DELL): no change

Any suggestion here ?

I don't have you system so I will show what my system does.

In my case I am plugging in earbuds and selecting such on the Waves Popup.  There is a Dimension window on the Waves where I can turn on or off that option.

If I go to Settings-System-Sound I have an option to open the Sound Control panel.  From there I go to the output device, Speakers/Headphones in this instance, and select Properties.  From there I can turn on/off Spatial Sound.

Other settings may effect how this works, there is a restore defaults button on the Advanced and Spatial Sound  pages.  If you want flat sound you should be able to set up a preference for that in the Waves equalizer and save it so it loads whenever the headsets are selected.  If that doesn't work, try setting the device as a default communications device.

The TB16 uses the Realtek USB audio device and as such does not come under the control of the Waves utility.  I just went through this yesterday with my system but I don't remember exactly what Waves could do when using the TB16.

The jack detection can be enabled with the Advanced menu on the Waves user interface.

I spent almost the whole day trying to isolate the root cause of the problem; I have deinstalled then reinstalled the Windows as well as the DELL Realtek drivers, and finally found the culprit for the 'permanent spatialization' issue:  the Waves MaxxAudio Windows app.

At the end of the day, I can now control spatialization for the 5530 built-in audio device with MaxxAudio, but NOT the attached dock TB16, where the symptom persists, just like if a default MaxxAudio EQ Profile is 'locked' in 'active' state; and the TB16 audio jack can't be selected in the MaxxAudio interface. This is apparently linked to the fact that now jack detection is completely dead: when I insert a headphone in either jack (5530 or TB16) sound continues to play from the computer speaker (and 'headphones' does NOT appear in the list of devices in MaxxAudio).

Jack/headphones detection work ONLY during boot: whenever I want to use headphone, I have to reboot the machine with the headphone connected ! Once I disconnect the headphones, sound goes to the internal speakers until the next reboot no matter what I try.

Obviously I'm running out of ideas (and my support engineer too, by judging on the time it takes for him to call me back...I'm still waiting sine yesterday)

How to get the jack detection work again ???

If that get fixed then perhaps MaxxAudio will be able to control spatialization on the TB16 audio also.

Try plugging the headset into the back audio output for the TB16.  It is normally for external speakers but seems to make adjustments available for the bass and such.  

Prior to testing, I had downloaded and installed the Realtek USB audio for the dock from the Dell site.  I plugged the headset into the back audio and was able to pretty much control the audio using all the Waves controls.

One thing a little strange, I notice is the normal custom controls are not actually listed and all I see is part of a Loudness option.  I can enable and disable the Spatial sound.  I can turn off Dimension in Waves.  The Equalizer does have an effect.  There should be a small blue option where it shows EQ profile where you can select different options to see if it changes.

OK, I will set my system back up and see if I can see what you mean by  'stealth' active Eq Profile.

Fair enough.

But then I see no way to disable the 'stealth' active Eq Profile which 'pollutes' the audio on the TB16 jack ?

Since when I'm working in the office in docked mode the PC itself is somwhat out of practical range [to connect headphones], I am forced to connect another USB audio device (e.g. Soundblaster) to get neutral sound ! Makes the TB16 jack pretty useless ??

Thanks for testing,

But there is definitely something wrong on my system: even when I use the PC "standalone" (no TB16), the jack detection doesn' work: 'headphones' isn't even listed in MaxxAudio: only 'internal speakers' appears in the 'list'; obviously then 'show popup dialog when device is connected' makes no difference.

I have to reboot the PC with the headphone connected for audio to be routed to them (and even then, MaxxAudio still only sees 'internal speakers'. And if I disconnect then reconnect the headphones, the sound goes to the internal speakers...until the next reboot with headphones connected !

I'm pretting sure there are some stranded things in the registry, but I have no clue how to properly clean them up before attempting to install the Realtek drivers (both for the internal audio card and the USB on the TB16) and Waves Maxxaudio once more.

As suggested by Support, I reinstalled the OS from scratch.

This allowed me to revert to the initial problem (the jack detection now works again): spatialization is turned ON by default, and using MaxxAudioPro app it can only disabled on the P5530 (laptop speakers or headphones) but NOT on the TB16 (front headphones jack or back line jack).

Interestingly, on the TB16, the type of spatialization changes as I change the type of Output Device (speakers vs. headphone), but other MaxxAudioPro controls have just no effect at all (EQ profile, MaxxBass, Details, and mainly Playback Enhancement ON/OFF switch). So it looks like the MaxxAudioPro app is not completely ignorant of the TB16, but the interaction is very limited and the most problematic for me is that Playback Enhancement can't be disabled at all.

I reckon this can pass below the radar of DELL Support (my support agent couldn't find this problem in his database), as most people may be satisfied with the default Sound Enhancements on the TB16, which is certainly acceptable in 99% of the usage scenarios like entertainment etc. and never notice there's a problem (speaking with people and AV pros around me, I'm surprised by the number of people for which basic audio issue can pass unnoticed). But it falls short when neutral, flat sound is required (video editing in my case); but there again, I think pro sound editors will work with a specialized audio I/O device anyway.

I just wanted to updated this thread to say that you have solved an issue that I've been trying to solve off and on for 6 months. Until now I've had to connect a USB audio device to bypass the problem.

I still don't know what I can do about this problem while booted into Linux, but I'm thrilled to have found the program responsible for this. At least I have a lead (and it's fixed for Windows).

The issue is that Windows gives you absolutely no hints that MaxxAudioPro is actually managing the audio. Here's a list of searches in the Start Menu that DON'T suggest "MaxxAudioPro"

Sound

Sound Settings

Audio

Manage Audio Devices

Spatial

Effects

Realtek

You can even find a menu option by right clicking on the sound icon on the toolbar that says "Spatial Sound (off)" which is useless because *this* spatial sounds setting is already disabled. 

There is NO mention of "MaxxAudioPro" anywhere in Windows control panel or driver information.

The only way to find the program named "MaxxAudioPro" is to search Maxx or the full name (MaxxAudioPro). Now there is plenty of blame to go around here. Certainly Microsoft for their search logic, but knowing this, Realtek COULD PUT SPACES IN THE PROGRAM NAME! That would solve the problem as I searched "Audio" multiple times and would have investigated the software if it ever came up. I had no idea this software was present on my system.

Ultimately it's not a problem that disrupts things frequently, but when I do need to do sound or video editing it has been a major stumbling block. 

Thanks for documenting your journey on this one.