Got around to making a quick and dirty model using the 5U case internal dimensions and the measured dimensions of the boards, my toroidy transformers, and brackets and such. Looks like there's room but you have to make best use of the vertical space. I don't really know what affects what like the real gurus here but I just tried to keep all the PSU's together and give the stacked amp boards their own space in the corner, as well as left space along the bottom back of the case for power plug/fuse/inputs/outputs. There's an inch or so left near the front that you might be able to shift everything even further away from the transformers as long as you keep all the faceplate controls in the center. As is, there's space to have the jacks or front power button offset.
And model is here for anyone to play around with. http://www.mediafire.com/download/t7jk13n7s2ky166/Amp+mock+up+6.obj