Equipment rack behind speakers: bad?

Done it many times (see my system). Best if the rack is centered behind/between the speakers since bass tends to build up in the corners, not the middle. And anyway, at the boundries (like the back wall) the energy transfers to the wall itself (which is turning the wave around) but there's actually less air movement to affect your equipment rack. In the picture of my system, you'll note I even have a Target TT shelf bolted to the back wall (OK, it's a brick wall) but the TT had absolutely no vibes transmitted to it.

The only downside -- it's a bit further to walk, so get a remote volume preamp :~))

Fairley, I also have a narrow 12' room. But even if it were wider, I think the best solution, both in terms of user convenience and system (electronic) layout, would be to put the amp(s), subs, elec. x-overs, etc, between the speakers and all the other front end stuff to the left or right sidewall, even with the listening position. You will use long ICs from preamp to amp(s) and short speaker cables -- which is the preferred way to do it IMO.