Its best these days to go with an amp with built in crossover control. My old school hifonics amps have them built in. The newer hifonics amps didn't impress me that much but that was the ones that came right after the ones I have and that was over 10 years ago so I have no experience with what they make now.

I know Rockford had gone downhill too back in the day but again no experience with their new stuff.

Im going with zapco from my research it seems to be the best there is at the moment for what I want to do.

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Just BMW's - All cars and trucks was two pages long
1994 318is
1997 528i
2000 323i
2001 X5 3.0 auto
2005 X5 3.0 auto
2011 535xi auto
2013 X5 xdrive35 Turbo
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Aftermarket E53 Radio Install