Hello Tim,

I am pretty sure that the two issues are not connected.
The sound gauge is there to play the sounds that are stored in
the Captain Sim folder, I think that with the renamed 707 gauge,
we are hearing the sounds in the Captain Sim\707\sound folder.

The engine and other ambient sounds are stored in the CS_B727-100\sound folder and are played by FSX, just like any default aircraft.
I can only suggest that you check the integrity of  this sound folder, it should contain 40 sound files and one sound.cfg file.
The folder should also be named sound and in the aircraft.cfg file, its entry for each aircraft should read sound=
Finally check your sound volume settings in the sound section in the drop down menu in FSX.
On your behalf, I have uninstalled and then reinstalled the aircraft to check the integrity of my advice and I hear all the sounds that I expect to.

Regards,
Nick