Can this amp be replaced?
What all does it power?
What are the specs?

I'm thinking of replacing the Bose sub in the rear deck and also possibly replacing the amp that's in the trunk.

 

You will be much more satisfied if you replace the HU and the amp.

 

Yes, it can, and should be replaced. The only tricky part is that the bose headunit outputs a differential-balanced signal, so you'll need an amp that can take it. All JL amps can. They're not he cheapest, but are readily available and good quality.

It powers the four side speakers and whatever you have on the rear deck.

Specs... well it's powered by like 14 (or 16?) gauge wire, so if it did much more than 40w RMS, it would start a fire, but it's advertised as something like 222w, but you know that's going to be peak watts, which mean precisely nothing unless you're a teenager in a parking lot trying to impress other teenagers.