I think the best car system I ever had was with a pair of EPI M120b home speakers, laying on their backs in the hatch of a 1973 Plymouth Duster and powered by a 12W/channel Sanyo under-dash cassette deck (remember those?) and a cheapo 5-band graphic EQ unit with something like 15w/ch boost made by a company called Royal Sound.
I'm fairly certain those speakers were 8 ohm but they put everything I've had since to shame. Unfortunately they were huge particle board boxes that basically filled the car, and the woofer cones eventually just fell apart from temp/humidity extremes and age (I bought them in something like 1978, mind you.)
The question - finally: Does impedance affect sound quality in any way? IOW, is there any advantage in SQ between, say, a pair of 2 ohm speakers vs. 4 or 8?
Someone recommended that I try Adire Audio Extremis drivers for more raw power, but they're 8 Ohm speakers. I have two pairs of MB Quart PCE216s installed and I think at least one pair is fried. Can I swap in a pair of Adires and run two pairs of speakers having different impedances off of the same four-channel amp without destroying the amp?