If your preamp or receiver has a low filter it will eliminate most of that extra excursion.
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Systembuilder, :-) , it is your turntable bearing. There is no reason on this earth to try to reproduce much below 25Hz with vinyl. Your sub is built to work down to 15Hz. Seems a little overkill to me, but it might work. I doubt I have ever had a arm/cart resonant frequency 5-8Hz. 8-12 is more likely. Those guys are not wrong, but they should have a clue about vinyl and subs. Movies and music are best treated separately, IMO.
I would suggest leaving the filter on at 35Hz and also set the crossover on the sub at ~40Hz. The sub rolls off at 12 dB while I'm guessing the filter is 24 dB. Combined, they may do the job. With these settings you need to move the sub around the room to find the best location. I would not go to corners as these will reinforce the low end.
FWIW, I have two subs that are the size of refrigerators and each has an 18" driver. However, the roll off very quickly below 30Hz and still move the walls when called for.