Precision 7740: separate volume settings for headphones vs. internal speaker?

Hi, I recently received my new Precision 7740 laptop, and everything works great so far except for one thing.  Right now, the headphones and internal speaker are combined into a single "device" - named "Speakers/Headphones (RealTek(R) Audio)" - for the purposes of sound volume (and other audio properties) management, with the single volume setting for that "device" applying to both the headphones and the internal speaker simultaneously.

There seems to be no way to separately adjust the volume: for instance, I can't find a way to mute the internal speaker while setting the headphone jack's volume to e.g. 30%.  The system uses RealTek hardware and drivers for sound playback, and I know that the old RealTek HD Audio Manager software used to have the ability to control internal speakers separately from (analog, non-USB) headphones.

It looks like the RealTek HD Audio Manager software is no longer being installed (or even supported?) - so has this long-time functionality been lost now (in the name of "progress", I'd have to surmise...) - or, am I missing something?  As things stand, I find the way the system is working quite inconvenient.  I don't want my system to be emitting noises by-default at the office, simply because I've just unplugged my headphones following an online meeting with audio-streaming...

Thanks in advance for any help.