Nice array of hardware. The ideal scenario is something with at least four HDMI v1.1+ inputs so the BDP-S1, HDXA2, and PS3 could send audio and video through HDMI with one input to spare, but that's hard to get. An HDMI v1.1 or higher receiver/processor will give you the greatest flexibility, but those are just beginning to emerge. There are a growing number of receivers around, but about the only HDMI v1.1 processors are Anthem's AVM50 and Statement D2 (don't know if the AVM40 has materialized yet, and the couple other truly HDMI v1.1 processors are at or above the AVM50's price range). Short of that, the 990 is going to be similar to any receiver or processor, although the DVI switching actually gives it a slight advantage. For what it's worth, here's one possible way to use the 990:

The HDXA2 and BDP-S1 both have 5.1 analog outputs, but of the two I'd probably use the HDXA2's SPDIF output and leave the 990's 7.1 Direct input for the BDP-S1 (since the Toshibas have a well-regarded high bitrate DTS output for the new formats). I'd also use the two DVI inputs of the 990 to switch the HDMI output of the BDP-S1 and HDXA2 (so both Blu-ray and HD-DVD have fully digital signal paths to the Pearl). The game consoles and HTPC can then go component through the 990, with optical or coaxial digital audio connections. Obviously there are variations on this theme, depending on which sources are seeing the most use - if the PS3 is getting used all the time and the HDXA2 only runs every couple weeks you might let the PS3 and the BDP-S1 use the two DVI inputs, or if you are watching BD movies in the PS3 as often as you do in the BDP-S1 you might use the two DVI inputs with the HDXA2 and the PS3...