OK now i researched it. The 650.6 has more crossover options. But the the Us amps has an subsonic filter. But has no high-pass crossover. Just mostly low past. But there is more to consider Like, How much room do u have, cus that zapco amp is long as hell. But the us amps is smaller but is power hungry. oh and also that us amp would be my choice but i would reccomend gettin and external crossover. That us amps has .006% thd at its rated RMS power!!!!!!!!!!!!!!!! That is an clean *** amp and plus i kno it do its rated power