If Steve says at least 4 inches that's what it will be. I discovered that I have a rack, currently in use with other equipment and some "rack cabinets" (smaller) so I can switch them around. The 10.5 (6 RU) referred to above was just some simple computation. I will certainly use his recommendations.

5 RU = 8.75 in.
6 RU = 10.5 in.
775 = 7.75 in.

Using 5 RU for 775 leaves maybe 1 inch above (allowing for feet---and I haven't seen the config'n for the MidAtlantic panel).

Another 2 RU = 3.50 in. So if there is at least 1/2 inch above the top of the 775 there would by calculation be 4 inches vent'n space with a total of 7 RU for the amp. Sp a 2 RU ventilated panel above the MidAtlantic should do. Your thoughts, pls.

Also, are there recommendations for required space above the 990? Thanks.