The 80's with the rubber feet are 40.25". I would think the rubber feat are better in the cabinet than the spikes would be.

I like the look of your system, not too sure about the SQ with the speakers mounted inside like that and with the foam it will get even tighter in that space, nit much room for the speakers to breathe. Any chance you could mount the M80s sticking out slightly from the wall and no doors?

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70