Bass distortion-Playing LP's only,,,,please help


VPI Prime----Ortofon Black Quintet (low output moving coil cart)-----Plinius Koru Phono Pre( loading at 20 ohms/gain at 66 db)-----Parasound Halo Integrated -----Martin Logan Montis speakers which have powered bass cabinets.

Using any other source component I have absolutely no issues. When I play an LP and increase the volume past 10 O'clock which is a little loud....but not ridiculously loud-I at times get this huge wave of bass distortion. I do have bass controls on the Montis's...and I have turned them down into the negative, but I still get what I previously described occasionally. 

Any and all help would be appreciated. This doesn't always happen, but its frequent enough to drive me crazy.

Thanks in advance.

krelldog
My apologies Krelldog. I didn't realise that you'd already tried negative values. Doh!

Memo to self: please read the entire post before commenting ;^)
How compatible is that Ortifon cartridge with the VPI arm?  Is it possible that this is just an arm mass - cartridge compliance mismatch that accentuates rumble on certain albums, and that it becomes more evident at higher volumes?  Have you tried a cartridge with a lower compliance on your arm?
The KAB rumble filter did not solve the issue. In fact my system did not like the addition. I am solving the issue by adjusting the bass controls on the Martin Logan Montis's,,,,,and moving the Montis's farther out into the room away from the turntable. I did try these adjustments before I bought the rumble filter.....but for some reason I'm having better results now. I'm still considering a isolation platform for my VPI Prime also.....thanks for all the suggestions.
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