I'm selling my recording interface - it's a Tascam US-122. 2 channels, RCA monitor outputs, MIDI I/O, uses USB. Does what you need an interface to do, and I've had it for a couple of years for this purpose, as well as controlling my monitors for everyday PC stuff and iTunes etc.
Being completely honest, it has some funny quirks. I have to unplug it when I'm done with the PC, or the computer won't shut down properly. It can also sometimes restart the computer if left idle for half an hour or so sometimes (but not if iTunes is running...). I'm not sure if it is a compatibility issue with my computer (I'm running 32 bit Vista), but it can be a little annoying. I've lived with it for a couple of years now, and it isn't hard to get used to these quirks (it involves unplugging the USB lead while it isn't in use, mostly), though they're less than ideal. Might not happen at all for the buyer.
But because of that, I'm only looking for £20 posted for it.