Yeah, that's a fairly standard avr which is not always the case with HTIB systems, and an active sub which also is not a guarantee with an HTIB setup. Basically real components that can be interchanged, one of the advantages of having components in the first place

. Looked at the system manual (HTP-593) and the speakers are 6 ohm rated, sometimes they're ridiculously low impedance (like 3 ohm).
Why a sealed sub? (your current one is ported/vented design) How big a room do you have? SVS' entry level subs are well regarded. A $400 sub you might look at is the RSL Speedwoofer10s. The Hsu VTF-2 mk3 is a bit more than $500 with shipping but would be another entry level sub I'd consider.