Is that another name for the Hazen Mod?

During Decfest I heard, I believe both the ZMA and MK4 with EL34, and I really didn't care for it. That said, I don't think the amps were biased correctly for the tube change, so it might not have been a fair comparison.

Also, I really think the KT-66 just kill on the Mystery Amp. It seems to do everything well, and now that I'm closing in on 400 hours, I think the high end dryness from when the amp was new is going away. I was going to verify this by plugging in my old 2 watt Zen amp and doing a quick A/B to help refresh my memory as to what smooth top end is.  :)

Sometimes, you just get used to something - so it's good to take something away or go back to something else to give you a fresh perspective - like cleansing the palate between wines/cheese.