I also would recommend wall mounting the tt. The heavy cabinet and solid floors has absolutely nothing to do with the resonance feedback you get into the tt. I went a diy route to wall mount mine a while back with heavy bookshelf mounts, a sheet of mdf, painted it black and stuck some automotive sound deadening pad to the top layer for further isolation. Worked like a charm and it was cheap.
The other problem is the turntable being placed right at the wall between the speakers that while esthetically it looks good and is convenient, it picks up a ton of the same low frequency energy through the air as well. If you have the option to move it out from right between the speakers against the front wall, that will help you a lot as well.
Even after those changes, I myself would isolate both the tt and the speakers. Seems to be a growing trend for speaker isolation platforms & pods.