Bungoblob

I have just inherited one of these large Sony amplifiers, and I was thinking of fitting it into a MY03 WRX saloon (when I get it) with a Alpine head unit/autochanger, PG 6.5" Components in the front, and possibly a sub in the boot. The amplifier has 6/5/4 on it - I assume it means channels? I want to know how to set it up as described above, and also is there a suitable sub & box on the market that will fit into the boot sidewell of the Scooby? I don't want massive bass; an 8" driver will be more than sufficient I guess. (Home set-up has 6" driver and produces plenty)!

Thanks in advance.

Tom