Thanks once again Ivan! I'm thrilled you were able to help!
The update worked and it resolved the issue I was having, HDMI would not handshake sometimes, and the audio would drop to stereo for some 5.1 sources. The cable required is a DB9 pinout to RS232 spec cable. I would not try doing this using a USB adapter to RS232; I've heard of this being a source of failures. It's a pretty standard connection for A/V gear -- my old Anthem D2V used the exact same cable to do ARC. It's hard to say what else was fixed since I was on a version over 2 years old. I'm sure someone at Krell has a changelog from 1.6 all the way to 2.0G, but that might be asking a bit too much -- besides, I'm happy so there's that.
FWIW, the S1200U has been the ultimate best pre/pro I've ever owned, and I've had just about everything (except Datasat). The S1200U sounds incredible, has the ability to create custom processing for every channel (EQ/DSP functions), and just the right amount of flexibility. Sure it doesn't have automatic room correction functionality, but it does give you the ability to do that manually if you have the appropriate gear and microphones. My only complaint is that it's a true Class-A unit and even in standby throws off a lot of heat. But I'm OK with that.
For a 5 year old unit, it's managed to stay in the game. It can upscale all sources (no 4K of course), process most everything (except Atmos); it does DTS-HD MA, etc. It is the best sounding pre/pro I've owned. Shame Krell made the changes they did the last few years. Their new gear doesn't do it for me. I'd love to hear if anyone has the Foundation processor and their thoughts.
This one is of the display on boot:
This is the OSD when something's playing:
