Sean's right, don't expect to find a bass null close to the wall boundry if you have conventional box speakers, even on the side (wasn't an option anyway, I know). If there seems to be no difference in bass energy anywhere within the area of possibility, then go ahead and center it to keep it furthest away from both speakers, except if one speaker is much closer to a corner than the other, in which case bias the rack away from the corner. In all cases, get the rack as much behind the plane of the speakers as you can for the sake of imaging and soundstaging, while still trying to leave a gap of at least a few inches to a foot between it and the wall behind to avoid the strongest bass reinforcement. Then look into an isolation shelf for your TT. Happy listening! :-)
