I don't have the new Plus, however, I've had the tubedac for a year now. Right after getting it I picked up an NOS Siemens E88CC. Actually I bought three of them and was able to sell the closest measuring two for almost the cost of the three so I got my single tube pert near free! This tube is absolutely NOT microphonic and raised the tubedac's performance a bit. A much bigger difference was noted when I got the 3XDC and plugged that into it's own Oneac Iso Transformer. Power cord is a humble Zu Birth but things really kicked up with that combo in place. I've since like MttBsh opened both the DAC and Power supply, liberally applied dynamat extreme and ERS cloth. Improvement about on level with the tube change. I found no effect from using a Herbies tube damper, however, I love them for my preamp! Since the purchase of the tubedac literally EVERYTHING in my system has changed, amp, preamp, speakers, transport, cables. I haven't even LOOKED at another DAC, save for the "new" Tubedac + which, when I talked to Scott about it he said, if you're happy with what you've got then don't worry about it, it's not so much an "upgrade" as it is simplification for him - one DAC instead of two and only a single board for all of his tubedacs.
About the system changes, everything was scheduled to change, but most things changed more than once in that time, specifically transports, cables and preamps. There was never any desire to look at another DAC. I love that little thing!
