I just upgraded my sound system. I installed 4 Polk Audio DB651's on my tower and pushed them with an MQ Quart Nau460. I liked how they sounded so much, I decided to replace the 4 cockpit speakers with the same Polk Audio DB 651's and decided to push them with a second MB Quart NAU 460. It sounds great. I'll add a third amp and a sub in the off season. I like how my system sounds and would recommend both the Polk Audio speakers and MB Quart amps.
Use good battery cable wire and 16ga speaker wire.
Oh and do it youself if you have the time and patience. It'll save ya a lot of $$$ plus you'll know it's done right.