Thanks. The shelf is 18" with the back on. The replacement cooling back extends that out 3.5" apparently. So 21.5" deep apparently. The Yammy 3080 is a big boy that shows 18-5/8" with wifi antenna. If the measurements are all true it leaves 3" behind for cables which will be tight but should work I'm thinking. Guess I could consider making a wood spacer if truly needed to gain another 3/4" to 1.5" of space, depending on how the backing fastens on. Looks like T-slots in the pictures, so should be easy enough if needed. The cooler panel has a wired thermometer to put on top of the amp itself.
In the absence of an earlier response, I went ahead and ordered one with the shelf unit to try. The model I'm getting is the one that is around 31" tall x 66" wide. It has 3 sections/doors.