Onkyo A9010 (~£175). Cheap, What HiFi Award winner this year. Should do everything you need. Only thing it's really missing is an Optical in, therefore no DAC. So you will have to your regular audio out port, whether thats motherboard audio or soundcard audio.
If you want an optical in on your amp, then the Yamaha Yamaha AS301 (~£189) accommodates this, and is a bit more powerful at 60w per channel to 44w per channel on the Onkyo. Or you can buy an external DAC that might do a better job, for cheap enough. I put a Soundblaster Z soundcard in my PC, picked up off the MM on here for £25. That is around the going price, as I have 2 of them now from here for that money. So that could be an option.
I too am looking for an amp for my PC, but I want to use my DJ decks too, so I need a second zone capability on the amp to drive the speakers I use for them. So that rules out the Onkyo. The Yamaha AS501 is a bit more expensive (~£249) or something than the AS301, But also more powerful at 85w per channel, so I am deciding between that, and the Marantz PM6006 (~£269), which is more again, but is meant to sound better, albeit less powerful at 45w per channel.
Or, you could go second hand, and just go analogue and cheap. I currently use a NAD 310 for my DJ decks. And whilst quite old now, it is a very good sounding amp, to me. But then again, it isn't really very powerful at 25w per channel. But it runs my B&W LM1's pretty darned good. I have no complaints towards the sound quality or loudness from it. I really doubt it is only 25w per channel in reality. And they are only worth something like £50 on ebay. So by far a cheaper option. If it had A/B speakers, I wouldn't be looking to change in all honesty.