Hi Nick,
Corners are really bad spots for racks, especially turntables because low refrequencies tend to resonate there. This is why one of the most common room treatments is bass traps in the corners to absorb excess low frequency energy.
If you slide the rack a few feet forward along the side wall that would help. Even between the speakers next to your amp would be better. Yes, large objects(e.g. TVs) between speakers hamper soundstage, but it might be a worthwhile tradeoff vs the corner.
If you play a test CD and read volume via a sound meter, you can easily see how low freq volumes increase in corners. Of course, by how much depends on your room. Cheers,
Spencer
