Isolating the tube amp on the floor or the shelf from vibrations is what matters more than where it is.
If the speakers and amps are sitting on a suspended floor,work on the underside floor joists and stiffen them up.
If the speakers are on a solid concrete basement carpeted floor,I think the amps placed beside them will perform better than on a less solid stand.
Of course there are costly equipment racks that will prove me wrong.
Short speaker wires and longer balanced IC are the way to go for me.
If the speakers and amps are sitting on a suspended floor,work on the underside floor joists and stiffen them up.
If the speakers are on a solid concrete basement carpeted floor,I think the amps placed beside them will perform better than on a less solid stand.
Of course there are costly equipment racks that will prove me wrong.
Short speaker wires and longer balanced IC are the way to go for me.