Delayed response to question addressed to me by Jafant. I have tried several of the 12AX7 (which I feel impact the sound more than the 6922). I have tried a NOS pair of Telefunkens that were okay witin my system. With my other components (Krell and Wilson), I have found that I like the Mullards the best. I have a pair of 10M which are just a hair better than the longplates in a couple areas, but I really like the longplates and don't feel that I give up much vs. the 10Ms. I feel that they are tighter in the bass than the 10Ms but not so vs. the regular ecc83/12AX7 Mullards. Technically, the standard mullards should sound virtually the same as the 10M. They are really the same tubes just that the 10M have gone through additional testing (Just like golf balls destined for the Masters, they come off the same lines with the only differences being in the additional inspections - and packaging of course). I have tried several others over the past 1.5 months or so and found that I like the Mullards the best - with my system.
For somebody buying a Calypso, I would say start with either the 10Ms or the Mullard longplates to cut to the chase a bit faster (especially if their system is somewhat similar to mine). Additionally, if on a budget, I would seriously consider the "other" branded Mullard longplates (which are the same) but will save some scratch.
For the most part I have ended up with Philips in the 6922 position and have been happy. I played around with a couple of others, amperex, etc. . . but not nearly as much as with the 12AX7s.
Again, I am not saying the Calypso is better than the Ref. 3. If I would have been willing to spend the money for the Ref. 3 I would have probably bought that over the Calypso. Now that I have the Calypso, I am not too eager to get rid of it and am still not willing to spend the additional money on the Ref. 3.