HDMI vs Digital Optical output for Universal playe

Actually no, HDMI is not just for multichannel sound. Modern HDMI can have up to four I2S streams, one spdif, and more than one 8bit video channel. It's the only standard interface that CAN carry I2S as I2S in itself has no standard connector.

OK, that said, if it's a modded player with a great built in DAC, just use the analog for two channel music enjoyment if it sounds better to you, otherwise don't worry about digital audio coming over HDMI versus a Coax and SPDIF that probably is not the proper 75 ohms anyway.

For CD listening, I'd definitely use a decent set of analogue interconnects. HDMI is for 5 channel. This way you will use the OPPO dac instead of the NADs. Just use the analogue by-pass in the NAD for music.

Agree with Kal on trying both digital options, but remembering that you've paid for around $1K of upgrade mods to the analog path of the OPPO, you should also try the stereo analog out option.

Hmmmm. Why not just try both? I really doubt there will be a difference for CDs.

Kal