My desktop PC has an excellent sound card with coax digital output.  I have a 5.1 speaker setup in the office, 5 boston acoustics passive mini-speakers and a powered subwoofer. 

An Onkyo TX-NR609 drives this setup.  But, it is way too big and heavy and overpowered, and I don't need video features.  

I just want an audio only amp, that can output 5.1, with coax digital input.  A bit similar to the proprietary all-in-one kits like logitech z906, but, I just want the audio amp/receiver functionality so I can drive my own speakers. It also has to be smaller than the Onkyo which is a full sized receiver. 

Anyone had experience? Actually quite hard to find, it seems that the market is mostly fulfillled by the all-in-one PC kits from companies such as logitech.