FalconGuy,
Yeah, you can't just change out the speakers. That's a huge no-no. The Mach 460 has its own crossover built into the head unit that divides the frequency spectrum to suit the speakers already in the system. After connecting my new speakers (before putting in the crossovers and head unit) out of curiosity I turned on the Mach head unit to see what it would sound like. It sounded REALLY bad.
I see you're in Northern VA too. Where are you located exactly?