Excessive woofer movement with a VPI JMW 9 ?

most likely you have the cartridge that is mismatch with the JMW9.
what cartridge are you using?

The problem is not endemic to unipivot arms. The problem is probably an arm/cartridge resonance that is either too low in frequency or too high in amplitude-- or both.

I hesitantly tried the KAB Rumble filter to address the same problem you're having - excessively pumping woofers. I'm glad to report it really did the trick, and with no sonic compromises I can detect. An added, unexpected bonus: my table seems much less susceptible to footfalls with the rumble filter in place than it was without.
Got mine here on A'Gon for around $160 - they turn up every now and then, and you could probably turn it around at no loss if you try it and don't like it.