In my opinion its a risk to get a pdx4.100. If it was the newer ones i'd say definately get that. But its hard to get a PDX F4 for that price.
http://www.m3post.com/forums/showpos...2&postcount=42
By the way, you don't really want to cut back on the amp with all the sweet equipment you're getting. You need to give them the love they deserve! Unless you find a good amp at a cheap price of course.
Have a look at the PDX, JL XD, and JL HD (very expensive though). These amps are all very good and are compact enough to fit under the "trunk" floor. This was ideal for me. Or if hiding the amp away doesn't bother you, you do have more choices.