You don't say much about the main purpose of this setup: is it just for music? movies? gaming? Is it for living room or a study? This is important, as your ideal setup may be different depending on the purpose.
By "using audio from the desktop" do you mean that you intend to use the PC as a source, or that your preference is to use the on-board audio hardware?
Now to some suggestions.
A good alternative to passive bookshelf speakers and a receiver may be active speakers (often called monitors). The advantages are:
- the amplifier is built in, so less clutter on your desk
- the amplifier is very well matched to the speakers
- monitors are designed for close distance listening
For applications requiring 5.1 sound (movies, gaming) you may start looking at dedicated sound cards - they will have the necessary decoders built in, and some are pretty well shielded from all the interferences.
For pure stereo output (music) a better option would be an external DAC, ideally with its own power supply and a couple of connectivity options (USB plus optical) - that would give your analog circuits the best possible isolation from the PC, which is probably the worst source of interferences in your surrounding.
I'm not giving you any specific models as this is hard to do without knowing the purpose, how much you are planning to spend on this setup and what kind of performance are you trying to achieve. If all you want to achieve is a noticeable improvement over the motherboard's audio+computer speakers, then $300 may get you there. On the other hand if only the best will do, then you may be looking at upwards of $10,000.