Receiver Recommendation/Help!!

I am currently looking to buy my first A/V Receiver, and really am struggling to make a decision...due to the overwhelming amount of technical information and choice available!! I am looking at the £600 to £1000 price range, and have seen the Sony STRDA5200, Denon 2807/4306, Yamaha 2700 and Pioneer VSX-AX2AV-S...

My other equipment is as follows:

Pioneer PDP507XD Plasma
Sky HD box
Toshiba HD-XE1
Xbox 360
Mordaunt Short 906i Speakers

I will be connecting everything except the Xbox 360 by HDMI cable, which will be connected by component. I may also be getting a PS3, so may require a receiver with 3 HDMI inputs. The most important thing for me is that the picture quality from each individual piece of equipment is not degraded by going through the receiver...but as I am a complete noob in this area, i'm not sure if this is possible when I am connecting everything by HDMI?? I also only have the two floorstanding speakers at the moment, but will be looking to add more in the future.

I have read that there may be problems with the video quality of the Sony 5200...or is this just with upconverted analogue pictures? Anyway, if anybody would be happy to recommend what receiver would best suit my other equipment I would very much appreciate it!!!

Thanks in advance!!