The only HDMI source that has to be connected to an AV Receiver are Bluray or HDDVD players as they only output HD audio in digital form over HDMI, which obviously carries both audio and video. You could easily route one of your HDMI sources e.g. sat/cable to the TV via HDMI and separately via digital audio cable or add a separate HDMI switch. In the case of Sky+HD connecting direct to the TV via HDMI is a good idea anyway as it gives you the option of using either the TV speakers for watching the news etc. and the speakers for when you want surround sound from those programmes carrying a DD soundtrack. The Onkyo HTX-22HD's amp is built into the subwoofer.
Unfortunately there is a shortage of decent 2.1 systems around or certainly the ones that can cope with LPCM audio from Bluray. Most have built in DVD players that would go unused if you have a Bluray player. Sony do make one, if I remember rightly.
LINK
Most speaker packages are sold as 5.1 and if you opt to buy separately i.e. a subwoofer and pair of bookshelf speakers, it gets more expensive. Obviously second hand is an option.
If you can raise a few more quid, have a look at the Focal Dome 2.1 package but it aint' cheap!