In the right rear compartment there is a black box that looks like an amp. Is this what it is?

 

Yep.

 

Do all models with HK Systems have Amps? Where exactly in the rear compartment is it located?

Thanks.

 

HK consists of different speakers and an amp. All head units (in the US) are the same.
The compartment is on the passenger (right) side of the boot. On the left side is a similar compartment - in the MCS it has a small tool kit. (not sure what the MC has)

 

Is there any I can hook a subwoofer up with the h/k system?

 

Or the OEM SIRIUS unit. Mine has it!

 

Easiest way is to just tap a pair of wires for the rear speakers and get signal from those. In fact that is really the only practical way of doing it without messing with the HK system a good deal.