Your not going to get much of an improvement, and in some cases you would be down grading by selling your PSA HCA 2 and buying any of the amps mentioned.
I would keep the amp you have and wait until you can afford an upgrade. But when you can afford an upgrade you might be better off with upgrading your source or speakers before your amp, which IMO is one of the better amps in its class.
I would keep Nuforce in mind as a possible replacement. They are class D monoblocks with a small foot print but you won't find many of these on the used market since they are all they rage these days. Lots of folks are selling their $5,000 to $10,000 monsters to own the $1,800 per pair mono bolcks.