Ah I understand.
Well here’s my thoughts, bass will travel through most things, not matter what speaker or sub produces the frequency, but you can avoid rattle and external noise through an isolation pad under a sub.
I think of subs as an extension of the speakers, not just a bass boom boom box.
But if space cannot allow, I completely understand, just wanted to make sure that you weren’t cutting yourself short of a great system
The Kef R900’s will get down and dirty with those 8” woofers however