Sounds gay but there's a "kit" to replace all the speakers in the M for a reasonable price.
BSW Speaker Upgrade for E46 BMW 3 Series / M3 Coupe -- Stage I Audio Upgrade | BSW: Audio Upgrades For BMWs
Front Speakers:
Rainbow Audio IQ Line 6.25" Midbass,
BSW 2.5" Midrange,
Rainbow Audio IQ Line 1" Silk Dome Tweeter
Rear Speakers:
Rainbow Audio IQ Line 6.25" Midbass,
BSW 2.5" Midrange
Bavarian Soundwerks Speaker Installation Hardware Kit: Butt connectors,
speaker connectors,
washers,
etc. - applicable for your specific vehicle
Extremely Detailed Installation Instructions:
Provides a guideline for the DIY'ers or professional installers. Step-by-step with photos!
BSW Speaker Upgrade for E46 BMW 3 Series / M3 Coupe -- Stage I Audio Upgrade | BSW: Audio Upgrades For BMWs
Front Speakers:
Rainbow Audio IQ Line 6.25" Midbass,
BSW 2.5" Midrange,
Rainbow Audio IQ Line 1" Silk Dome Tweeter
Rear Speakers:
Rainbow Audio IQ Line 6.25" Midbass,
BSW 2.5" Midrange
Bavarian Soundwerks Speaker Installation Hardware Kit: Butt connectors,
speaker connectors,
washers,
etc. - applicable for your specific vehicle
Extremely Detailed Installation Instructions:
Provides a guideline for the DIY'ers or professional installers. Step-by-step with photos!