Blimey... Sounds like you did all the right stuff...
Does the Xbox still boot from 'proper' game discs? When you first turn it on, and it displays the big green Xbox logo, does it say evolutionX or executer (or something similar - can't remember exactly) in white letters underneath? You can tell if the chip is running cos the white Microsoft text has been replaced.
If your solder job on the infamous D0 point isn't working, the Xbox will boot without the mod-chip. So normal discs will work, and music CD-RWs, but cos the mod-chip isn't being used, none of the unofficial stuff will load.
If you don't see the executer or evolutionX white text under the XBox logo at startup, you'll need to re-solder just the D0 point. If you do see this text, I suggest rummaging through the
www.xbox-scene.com forums for more answers.
Your CDRW media *should* be OK, but it does depend on the drive. Some drives are more, er, accomodating than others. Don't give up tho - it's definitely worth the effort
[edit...]
Just noticed that you already flashed the BIOS. Did you do that with a programmer, or with the chip installed in the Xbox? Have you been able to make any CD-RW non-music discs (such as a BIOS flasher) work?