A stereo integrated ampflier is just 2 channel, analogue- but will sound the best. For a 2 channel "Hi-Fi"
A av amplifier is a amplifier with 5 channels, video switching, bass managment, pro-logic, dolby digital & dts processing, digital inputs. a av receiver is the same except it has a tuner built in.
You cannot wire speakers directly into your soundcard, there is no poweramps. Since you want multi-channel I'd get a av amplifier/av receiver.