techweenie: here is what I use in my 964.
http://www.woofersetc.com/product.asp?0=270&1=609&3=1331
$ 125 each.
Also check out
www.madisound.com for great raw drivers if you already have grills.
Bought most of it off ebay and etc. and do most of the install stuff myself, but I am having shelves profressionally built for the 964 now because my sub amp is too large to fit. That's why I have that Pheonix Gold in there for the time being.
Stereo is on only half to 1/3 of the time. I took it out today to exercise it with the top down. I love to listen to it with the top down. I turned the stereo on for about the last 5 minutes of a 30 minute drive.