Things are going well with the speaker isolation. In addition to the direct benefits already described the in-direct benefit is that it's a lot easier to move the speakers around generally and so play with positioning and fine tuning
Recently I also acquired a couple of IanMac filters from Callen for the CDP and Pre. Added these on and there was a definite difference but hard to put my finger on... the music seemed more 'colourful' and 'rich' but was it an upgrade? Yes, but hard to tell instantly what had happened.
I sometimes think there are 2 sorts of upgrade as shown here. Take an example:
1) move speaker closer to wall -> bass level increases. Easy to hear.
2) the other sort is when the sonic picture changes but it takes a while for your ears to fully adjust and take it in.
So after a few weeks with the filters I can honestly say the system has never sounded better