I've been watching TV OTA using ARC for audio through 975. Confirmed 0 ms lip sync delay. No problems with this. Nice feature and I'm happy it's there.

(Glad it's available because I'm having problems with 975 - hum on all channels when anything plugged in to any HDMI. I next created a bunch of hand-off issues moving cables around and ended up watching a couple NFL games OTA with 975 playing audio via ARC. Then I figured out what I did, but I've still got hum. ARC audio works great though!)