Thanks for the kind words. I did not get to try a properly functioning JC2. The issue with the JC2 I got was that the gain was somehow very high - at least that was what I was told by the parent firm.
As for the Rhumba - you do not have to adjust any gain. It is just plug and play. And of course you can try different 12AU7 tubes that you like, which are easily accessed through the cover on the top.