Stumbled upon this today, if you would like to restore the old volume control option (incl. link to the volume mixer) simply enable the following registry key:

  1. Open Registry Editor.
  2. Go to the following Registry key:
    HKEY_LOCAL_MACHINE\Software\Microsoft\Windows NT\CurrentVersion\MTCUVC
  3. Create a new 32-bit DWORD value named EnableMtcUvc and leave its value as 0.
  4. Sign out and log in back to your Windows account. Alternatively, you can just restart the Explorer shell. Actually, for many users this tweak works instantly, so try to click the speaker systray icon first.

The source for this fix is below, with screenshots

http://winaero.com/blog/enable-old-volume-control-in-windows-10/