you have to use bmw specific stuff. BMW's use 3ohm speakers, if you use standard 4ohm they'll sound like shit.
Either rewire your whole stereo, get OEM replacements, or use BSW speakers (bmw specific upgrades)
I run a canadian HID kit company, if you have any questions about hid kits in canada or would like to check out our products please contact me here: http://absolutehid.ca
Hot: 2001 Estoril M Roadster
ZCP 19's michelin supersports, ZHP knob, JL 8W3
Cold: 2002 TiAg M3 6mt
ZCP 19's michelin supersports, deoranged, dechromed, led tails, ZHP knob, UUC SS v3, GROM, OEM 18's w310's,