Just a quick update on this topic.
I am running Simply Stunning 2.0.2 ESE53 with Adamz's low voltage kernel.
It appears that the in-call audio level adjusting DOES work- both with the regular speaker (headset) and while on speaker-phone. I tested it out several times by calling myself (from the cell phone itself and from a landline) and calling other people and other people calling me. (Yeah, I know thats alot, but just wanted to cover all bases)
So not only does the indicator change, but the actual volume level changes as well.
Not sure about the BT functionality as I rarely/never use it. So for me at least, all seems to be working well.
I think the OP was before any of the 2.1 ROMs (ERE25 & ESE53) came out. Not sure if this has anything to do with it, but most likely it does.
Hopefully any of you who have 2.1 ROMs can re-try this and see if it works for you as well.
Worked on stock player, Pandora and '3' (Cubed).
I used Root Explorer to copy/paste/backup all used files.
A quick note, if I simply re-named the files currently in the system/bin and system/lib to /filename.so.bak.../ap_gain.bin.bak...etc etc (meaning leaving the current files in the folders, just essentially backing them up..) and then pasted the new audio files into their respective place...I would get stuck on the "M" during a reboot. There was no way around it. Ended up doing a nandroid restore.
BUT...if I just deleted them, then pasted the new files...everything worked well.
Quickly ran out to my car and listened to the new sound on my car system.....and.... I'm impressed!
Would be really cool to have a base equalizer with say...10 frequency bands....with sliders to even fine tune more...but what I have now is definitely better than stock!
Good luck!