Diamond is not all it is said to be. Like Luke said look around. For big bass and sound quality I like Rockford,but they are a bit on the expensive side.But I forgot you said you wre going to get diamond so this should not matter. If you buy P3's youll come out cheaper bass loud and have decent SQ
The diamond audio subs SOUND WAY BETTER then rockfords any day of the week, you jsut have to listen to them in a good box. There is no difference in teh D9 and the TDX sub, other then teh color of the cone material. If you are looking for A LOT OF BASS these are NOT the subs for you though.