I have a 950/770 combo and have never had an overheating problem. All of the speakers I drive with the 770 are 6-ohm nominal impedance.

I would think that 8 inches above the 770 would be plenty. This assumes that there is also sufficient room to allow air to enter underneath the 770, that the air entering the 770 has not been pre-heated by other equipment, and that your rack is an ‘open’ environment that doesn’t partially trap heat in. I know some people with closed racks that use a fan or two to intake and/or exhaust air from the rack and others with fans on their power amps that are in an environment where they are not ‘free to breathe on their own,’ regardless of brand.

Seeing 770 overheat problems reported here is pretty rare. After a thermal shut down, how hot does the warmest part of the top of the 770 feel to you? Is the heat pretty even across the top, or mostly coming from just one channel’s heat sink? If just one channel seems to be the culprit, try switching that channel to another location a few channels over, both input and speaker, and see if the ‘hot channel’ moves to the new location. If you do have a single hot channel that follows a particular speaker connection no matter which amplifier channel is used, I would wonder if that speaker were still presenting a proper impedance.

Outlaw tech support once told me that the channel labeling on the back of the 770 was just for convenience and that I could use the channels in any order I wished. Perhaps I’m eccentric, but because my center, left main and right main will have a higher continuous output than the other four channels, I separate these ‘hottest’ channels by connecting in this order across the back: right main, right side-surround, right back-surround, center, left back-surround, left side-surround, left main.

Regardless of what you find out, if the problem is in the 770 and it needs replacement, I’ve found Outlaw customer and tech support to be great.