if you only have a desk to place things on, a 5.1 setup will be not much better sounding than a good 2.1 or 2.0. surround sound relies on being placed around you for it to sound good. it sounds like you would be better suited to stay with 2.1/2.0.
if you went unpowered (which needs an amp of some sort). bs22, mb42, klipsch kb15, etcetera.
if you went powered (plug and play) av30/av40, cr3/cr4, a2/a5, pb42x
if you want a subwoofer, dayton subwoofers are cheap yet not bad.
swan hivi set also isnt a bad little 2.1 set but isnt cheap.