Heyho, hello!

I've got an Asus P5B mainboard (bios 1202) and 4x1GB F2-6400CL5D-2GBNQ G-Skill Memory.
I already know that Windows XP can't adress more than about 3,25 GB memory and I already switched my chipset timings in the bios manually to
5-5-5-15-4-42-3-11-7-13; ddr2-800 and voltage 1.90V for the memory...at the moment I run the board only with 2GB in dual channel and with these timings the system seems to be stable and runs well---
My wish is to get the most possible ram amount to work, just because I am working with music progs on the pc and every single mb of ram memory counts...or the fastest and best possibility I can get......problem is that the bios (not only windows or anything, both OS and BIOS!!) just says there are 2688MB of memory either there are 3 or 4 GB in the slots....and I do not know if there is any dual-channel mode left when there are only 3 chips in it or if I need 4 of them to have the best solution or...arrggghh!
Please...someone with more knowledge needed!

Thx for your help in advance...Cya!

P.S. Vista is no solution, coz the music progs do not run on this OS!