I used 75 as suggested in the manual though will try with 85 to see if there is a big difference.

By stacking, I mean "directly on top" with no spacers. It isn't too hot right now...more warm than hot.

I hadn't thought of spacers. I need to make sure it looks nice since this is in our living room. I was thinking of using squash/racketballs cut in half, though I am not sure they would take the weight. Any suggestions other than wood blocks?

Thanks for the suggestions. I haven't done any serious listening yet, though initial trials with a few CD's and one DVD have been very positive.