Receiver options
A mid range receiver like the Yamaha RX-V659 or HTR-5960 would work well in your system. For playing music or movies from the PC, use a digital optical or coax connection to the receiver for audio and connect the DVI, HDMI, or VGA video connection directly to the display. If your PC sound card doesn't have a digital output, you can get a Chaintech card with optical output for about $30 from newegg.
Your ascends are good speakers so in your budget I would go for a quality receiver with a good amp stage vs. one with HDMI switching, etc. that is lacking in audio performance.
I also recently got the Oppo DV-970HD for use with my 32" LCD and would recommend it.