I hope some folks still can help with this.
I have a similar issue to the last poster. I have a 770 with a Samsung TV and a TiVo Premiere. TiVo goes to TV hdmi.
I hooked up the 770 to the tv via the arc hdmi on both ends. I was able to find the option to start the 770 in arc when turned on.
I couldn't get surround to work, the center was silent and the options on the 770 are confusing. I blindly tried lots of combos, no joy.
I then went to the samsung options, and changed the digital audio out from pcm to dts neo 2.5, the only other selectable option, and JOY! Surround suddenly worked and sounds great.
Here's the problem... the setup is not robust. If everything is turned off and back on, it seemingly reverts to pcm even tho it still displays dts. If I change it and change it back, it suddenly works again.
I don't think the TV is at fault. The problem occurs even if just navigating certain menus on the 770 (while changing nothing on the tv) and I have to do the same annoying thing. Also, when using an older Sony system, albeit via optical not arc, I never had to do anything to get it all to work, the TV was set to pcm and I didn't use the tv dts option.
Is it possible I need to mess with options on the 770? A lot of them confuse me! PCM fix, bitstream, hdmi audio out on or off, etc... too many and the manual explains nada.
I don't want to have to go into tv options every time I turn on the TV!