Tube dampers in Aesthetix

Anyone any experience using tube damping rings or the like in an Aesthetix Calypso? Currently running Mullard and Sylvania 5751
I oncer queried Glenn Buckley of Aesthetix on this point. He said he preferred not to use dampers on the tubes. Another of his thoughts -- replace the 12AX7s with 7058 type tubes. A little hard to find, but cheap and, in my experience, very good sounding.
Dopogue, many thanks for your response