How close is too close for a truntable to speakers

If your floor is a concrete slab, using a good rack or TT stand is OK. Otherwise consider a wall shelf (Target) mounted to (preferably) an (outside wall) constructed of (preferably) brick or concrete block. Interior stud walls are OK too if they're not too large (in area) and don't vibrate too much -- they're still better than wood joist floors.

As for turntable location, especially with Maggies, which spread the wave over a large area (a good thing), you can actually put the TT between-and-behind the speakers (on the rear wall) or, if that's not convenient, then on one of the side walls near the front (listening end) of the room. The front wall (behind the listening position) is OK for a good rack on a slab, but not for wall mount (unless it's a masonry wall) because the bass energy is most intense against that wall.

Nsgarch has covered some good, basic points. Just to expand on his last point, it's really going to depend on your room and it's bass response. I have found in my room that there is a large bass null zone just behind my speakers for about 1 to 1 1/2 feet. This is why I positioned my amps next to and outside of each speaker. Then, moving farther back toward the front wall another foot or so there is huge spike that grows as you move up against and towared the center of the front wall. These null and spike zones are pretty easy to find with Radio Shack SPL meter and a tone generator. I use the test CD that came with a copy of CARA software. Search over at AA in the Rives Acoustic forum for more recommendations on test tone CDs. Obviously you want to avoid putting your table in a spike if you can.

fixed the title of this thread :(---- Sorry

Dan_ed's got it right - find a null spot in your room and put the table there. My LP12 is sitting on a wall shelf directly behind my left speaker, in a bass null. I have no problems at all with feedback or other sonic impingement.