How good is the Obsidian plinth of Technics SP10 ?

I have an SP10 MK II with the Obsidian plinth. I am using a Basis Vector arm with a Soundsmith Zyphyr MIMC. My audio room is on the second floor so I have always mounted my turntables on the large Target  TTW1 wall mount rack. I replaced the cheap target shelf with a 3" maple platform.
I removed the crap feet that came with the obsidian plinth and have the original version of the stillpoints pointed up to the plinth. I had my SP10 rebuilt by Hans Lazuadi as well as he fabricated a brass mat that was screwed to and balanced with with SP10 platter. My system also has two Seaton Submersive subs that I use in both stereo and surround modes.
Using the subs in stereo mode I can drive the volume up pretty darn loud before I get any sort feedback issue from the turntable.
   I too have wondered about other plinths but have been hesitant to invest big $ in a custom plinth not knowing if the incremental improvement would be significant.
  I will also comment that recently I have been ripping my vinyl to DSD128 using the Korg DS-DAC-10R. I find the playback of ripped vinyl via my Lumin A1 to be at least equal to playing the vinyl and superior in the aspect that I can truly crank the volume with two subs well beyond reason without any feedback.

To Downunder:  The two subs I am using in stereo mode are the Seaton Submersives. They are dual 15" subs with a 3400 watt amp each. They are flat to about 10-14 hz...So they can definitely excite the cartridge/tonearm/table system into feedback with a record with a lot
of low frequency info at high volume (think Donald Fagen - Morph the Cat)...It never happens with just my main speaker running full range (Green Mountain Audio Continuum 3) which have a -3db at 27Hz.