I have the same setup. I haven't opened it up, but if you will notice, the sub is only active when you are faded to the rear speakers. My guess is that the sub has a crossover in it because of the above and because the sub is an option, but the receiver is the same with our without it.
So, I would bet that the receiver is a pretty basic 4-speaker output.
Let me know if you can confirm or refute this...
01 Sport, front drum brake & birfield joint conversion, custom '4 Wheel Drive' stickers, neon washer nozzles, chrome type 'r' oil pan bolts, wooden bead seat pads, racing exhaust tip, offroad license plate frame,
lots of misc. stuff (2.5" Skyjacker springs, 1" BL, 1"MML, Custom flat tcase & engine skid, RE arms, Skyjacker shocks, JKS Discos, Superlift Trac bars, Garvin bumpers, Warn 9.5ti, Lockright & trac-lock, 32" BFG KM's, Kilby & warn skids, EOR rocker bars, cowl snorkel)