I need louder sound for C902

[Max312]

Hey everybody,

I just got a SE C902 vodafone branded but not locked.
Before that I had a K800i and now i am pretty disappointed about the sound volume. It just is not loud enough! Espiecally in a loud environnement like my daily subway ride it is pretty annoying. The K800 was louder. I flashed my k800(dont think i am expert though..., I had to google everything and it took me like a week^^) so I am not sure if that was its original sound or the flashed sound.
Anyways, I know that I can increase the sound with a flash of the acoustic files. Is that right?
But from my google week for flashing the k800 I remember that I would loose the warranty for the phone when I flash it. Is that also the case when I ONLY flash the sound drivers/acoustic settings or whatever. Because I dont really want to flash the Firmware and dont want to loose the warranty.

If my plans (louder sound, but no firmware flash nor warranty loss) would be possible, could you once you are typing anyways give me a tip on which sound drivers I should use and how I would get those on the phone, please?

Thank you,

Max

EDIT:

Oh, I forgot something, sorry:

i bought a Bluetooth wireless stereo headset and love it. So if possible I would like to increase the sound volume for this headset(it is not the headset that makes it quiet, when I use it with the K800 it is clearly louder). If this is not possible I can also use a regular headset, though