No problem drewy1!
Was the 875 in the 4-ohm or 6+ ohm mode when it shut down?
Here's a simple test....
If you can, pull the 875 out of the AV rack so that it's not confined. See if you can then get it to shut down at the volume levels that you wish to drive. Don't overdo it, but get it back to the volume level you want.
If it doesn't shut down, then it was the confined space. Get a new AV rack or explore the many DIY fan options that Onkyo users have come up with over on AVS.
If it does still shut down, then it isn't due to the confined space. If that's the case, then you may need to either get a different AVR or go whole-hog and buy an amp.
And another tip...
I know that with the 876 there was actually a "secret" set of key presses (on the front panel) that would display the AVR's internal temperature. A lot of people with heat issues would use this to see how close they were to having thermal problems. And to monitor how their DIY fan solutions were working. I don't know what it was, but if you peruse the AVS forums you might find something similar on the 875. Since they're so closely related, I'd be surprised if the 875 lacked this feature.
