I'm quite happy with my pca-2/hca-2 combo. However, my speakers are a bit on the warm side (eminent tech LFT-VIIIAs). I have never experienced any lack of power with my inefficient speakers 83db. However, i do live in an apartment and never go too loud. I will say that i prefer the hca-2 to an aragon 4004mkII i previously had. I found the hca-2 to have better low end control, extension, and weight, have warmer mids, and throw a more realistic soundstage.
I've also done mods similar to modwright's mods on the hca-2 (< $100 in parts). They do make a nice improvemnt over the original and are relatively easy to do. Over at the reference audio mods forum, they've laid out pretty clearly what mods they do to the hca-2. So, if you're handy with a soldering iron, there are nice improvements to be had for a relatively small investment.
A couple of tips: Removing the bolt from the transformer and lifting it from the chassis removes quite a bit of the hardness many associate with this amp. The amp is really very sensitive to power cords, too. The best match i've found so far is a ps audio lab power cable.