As a former 970 owner and a current 990 owner, let me throw in my 2 cents.
Both the 970 and the 990 are wonderful pieces of gear.
Outlaw audio may not like me saying this but, I would recommend to anyone to grab a 990 NOW while they last. Don't wait for the new processor. At $699, the 990 is a heck of a steal. That's almost $400 less than what I paid for mine.
If you are waiting for "the next thing" in audio, you will be waiting for many years before content catches up. Not to get any holy-wars started, but just think how long DTS, which I find superior to DD, has been around and see how much content you find. DD 5.1 will be the de-facto standard for a long time. I plan on keeping my 990 for as long as I can and I do have a 7.2 system. If 7.1 source material ever catches on, I'll just look for a source that can do its own decoding and take advantage of the 990's analog inputs.
By the way, when earlier Sunfire Theater Grand processors (and some Classe) had similar problems, they were never really able to fix the problem entirely either.
So, in summary, I would upgrade to the 990 and the price drop alone would justify whatever you do with the 970 (keep it, sell it, gift it).
Just my two cents...