Agreed with Paraneer. You need to ditch the HT receiver if you want the best sound. Also replacing the SA-9100 with a
DO NOT connect both sets of speaker cables to your speakers.
What would probably be better is to get a device that will convert your digital to analog and send it via standard analog RCA jacks into your SA-9100. Since I'm still not sure what type of digital device you are using for the front end of your digital rig, I can't say exactly what you need. However, since you are ultimately using 2 channels of amplification and 2 speakers, you don't need a multi-channel digital front end.
So again, what is the digital device you are using to store/stream your hi-res digital files? Does it have optical, coax or USB digital outputs? If so, you just need a DAC that accepts optical, coax and/or usb.
Keep digging. There are plenty of quality newer integrated amps that have DACs built-in. Otherwise, a DAC to convert your digital to analog, combined with your existing SA-9100, or a new high quality integrated amp, would do the trick.