Subwoofer rumble issue

What turntable do you have? Some are more prone to this issue than others. Where is the turntable in relation to your speakers and turntable? 

It might be your turntable.  I had a Concept and it was super sensitive to footfalls.  I couldn't walk anywhere near it without the arm jumping around.  Granted, I have springy floors and it wasn't very well isolated, but I've had a number of tables before and after it that didn't have that problem.  I seem to remember issues with what you've described at high volumes also. 

It's surprising and unfortunate, because it does seem to be a solid and well built table.  It may have something to do with the magnetic bearing tonearm design.

There are a number of reports of this issue if you do a web search.  There are also many who love it and report no problems with it.  There seems to be a consensus that it needs to be really well isolated.

I really liked mine and wanted to love it, but it didn't work in my less than ideal setup where many other tables have worked great.  You'll notice I use the word "seems to" a lot in my post, there's obviously some supposition on my part, as I was never able to figure out how to get mine to work satisfactorily in my system and I know many others have that table and love it.  Do you have another table you can try out and see if it has the same issue?

Buy the svs sb 3000 with control app for under $1k delivered

Buying a bigger and more powerful sub is not going to fix a turntable problem.

Glad to hear you got it worked out and thanks for sharing the solution.