Okay, your full model name is Inspiron 17R SE 7720. Dell does not provide a Windows 10 audio driver for that model, but you can get one from the Realtek web site. No telling whether or not it will have the features that you had before changing the laptop's operating system.
Go to the Realtek downloads selection page. www.realtek.com.tw/downloads
On the page click on "High Definition Audio Codecs".
Check "I accept" and then "next".
In the column named "Description" find the file named README. That has the instructions for installing or updating.
In the column named "Download", click on one of the server names to download the readme file.
Go back to the column named "Description" and select your operating system (and whether it is 32bits or 64bits) from the top 2 choices in the list.
In the column named "Download", click on one of the server names to download the driver.
I had exactly the same problem on my 17R SE 7720 (MaxxAudio settings & sub-woofer not working etc) and managed to fix it easily:
Go to the Dell support page and enter your service tag. Then go to Drivers & Downloads --> Find it Myself. Change your OS from Windows 10 to Windows 8.1. You'll notice that an Audio category appears underneath. Expand this and download the IDT High-Definition Audio driver. Run the file and it should re-install the correct drivers to make your speakers inc. sub, work. Your computer will need to restart after the installation.