Spoke to Jim at Outlaw, he straightened me out. I had been messing with the very last option under the 975's "Audio Input" menu ("HDMI Out to TV") and he said to leave it off, that it was not relevant to the ARC functionality. That seemed to work, now I can switch between the two inputs to the TV (Antenna and the HDMI ARC) while retaining audio. I am still experiencing what appear to be handshake issues, so will do a bit of troubleshooting there, but the connections and settings appear to be working. Thanks, everyone!