Lots of folks are complaining about the new sound system and the level of configurability. The Miles Sound System is on the flight path that gets the game to somewhere the HTC folks want it to be. So the nut of the problem seems to be what is configurable and what is not.
It appears that the sound sliders were done along logical lines, music, external, etc. The problem is that the logic doesn't follow what is useful from the cockpit. My suggestion is to make the sliders available along that line.
First, put sounds that are "constants", that is the ones that go on for long periods, essentially looping on one slider. These are sounds that a user has a high likelihood of wanting to tune down as they really contribute to sound fatigue. These would be your own engine and the air raid siren. No one wants hearing damage from a long term beating by those.
Second, VOX. Communication is key to the game. If you can't hear your teammates its pointless to have VOX.
Third, internal A/C or vehicle sounds. This would be wind, flaps, gear, buffet, etc. A great deal of the flying experience, since we don't have the priprioception, seat of the pants feedback is by audio cues. Having these not available or obscured by other sounds is not helpful.
Fourth, external sounds. Other vehicle engine sounds, naval guns, puffy ack, etc. These are relatively temporary but you want to have the sound level to where you are aware of them. You don't want to be deafened by them suddenly either and so they rate their own slider.
These are in order of priority, but I think the first is the most important. No one wants to be physically drained by being beaten by a horrendous sound over long periods. That is wearing and takes away the enjoyment of the game.
I hope that helps!
