I think the basic assumption here is wrong. The sound being transferred upstairs will be almost entirely airborne not structure-borne.
So move the speaker away from a room boundary (floor) by putting it on stands means it produces less bass, so less bass is heard upstairs.
Whether the stands couple or decouple makes no difference to this as structure-borne transfer is not the problem. There will be some but it will be totally eclipsed by the airborne transfer.
Current Lash Up:
TEAC VRDS 701T > Sony TAE1000ESD > Krell KSA50S > JM Labs Focal Electra 926.