Since the 990 has a serial port, do we know if there is an accessible protocol for control to allow integration with home automation systems?

I don't think we know yet. When I was checking the Sherwood's manual for info on the USB port, I also looked at the entry about the RS-232 port - it hints at the capability (as if it could be done if a software update were released), but doesn't go into detail beyond that except to say that they only recommend that professional installers try to implement that sort of programming.

I have my a/d/s/ 4 zone whole house audio preamp integrated with my home automation system via RS232. I'm aiming for a high level of automation and integration in my new home theater, and having this feature would be great. I honestly don't know how many other people are going to care, though, so I probably shouldn't hold my breath.

Since I am a professional firmware developer, they could hire me to implement that feature in exchange for some equipment.

So, the manual mentions that the RS232 port can be used for automation systems. No other mentions in the manual about protocols, though.

Maybe they'll publish it as a separate document?

Or it could be part of the "not ready for prime time" additions still to come.

I thought I saw a post from Scott at some point saying that they were getting that information ready - most likely in a separate document.