Good info. I presume you're running from your computer to the HDMI in on the HDelity box? From there, you should be running either Coax RCA or Optical S/PDIF from one of the two connectors in the middle marked SPDIF. On the other side of the box there appears to be a switch, which I can only guess determines if the audio being output from the HDelity box is going retain 5.1 encoding or be down mixed to 2 channel stereo (not all devices will accept 5.1). Make sure the box is set for 5.1, not stereo.
Your amplifier is going to need to support the particular 5.1 encoding you are sending to it, either DTS or Dolby.
Are you sure that you are outputting a 5.1 encoded signal from your computer and that your amplifier supports the particular encoding you are sending?