OK.
Reducing transmission through HVAC isn't going to happen via speaker isolation - sorry.
If you're speaking of reducing vibrations in the speaker cabs themselves, that isn't going to happen either other than clamping them somehow to damp them - or potentially treating the inner walls of the cabinets.
To decouple from the floor, I'll give a shameless plug to our stand. It's designed specifically for that with a bass absorber built in. Then spike the speaker to that for rigidity.
Bryan