If you are going for HTiB, and you want to hook your PC or HTPC to it, then make sure the HTiB has the input for it. For an example, not all GPU can push audio through HDMI, and if you are using such GPU, then you will need another audio input on the receiver.

I maybe been living in a cave for too long, I have never heard of a PCI amplifier card before...pardon me. However, I do know that there are active speakers (with build-in amp) on the market, half the size of most of the floorstander. You can connect it straight to your sound card. It's just like an oversized PC speakers. My dad is using it in his bedroom, and it sounds good too. I mean if you compare with normal PC speakers.