I regret selling my Snappers, but I had to as I was frustrated with the tube situation. This was before Gold Lion KT77s were introduced, and just when Black Treasure KT77s were coming in. I had already blown money on several octets of tube to try to duplicate the stunning sound I had from the original factory tubes that were Groove Tubes E34Ls. These were copies of the original GE E34Ls which were higher power than EL34. Groove Tubes contracted JJ to build these tubes for them using the original GE equipment and raw materials that Groove Tubes provided them. Of course JJ fucked it up and after a couple batches more than half of the tubes were grenades. JJ also started selling their own JJ E34Ls, maybe those were the good ones. Manley built special testing jigs inhouse to filter out the bad tubes that Groove Tubes own testing passed. But it was an impossible situation the tubes would still grenade after a couple hundred hours. So Manley bailed on the GT E34Ls for which the amp was originally designed. Mitch Margoles, the Snapper designer, was also involved in the Groove Tubes reissue of this tube, so the amp was intended specifically for GT E34Ls. I got 2000 hours without a problem from my original set, but using them on capacitive load Quad 2905s revealled their weakness so I ordered the second set (from Manley) and had problems from the beginning, and some grenades broke my amps several times. When Manley finally sent me a free set of EH 6CA7s I was disappointed at how blurry they sounded. Definitely not Snapper-worthy. I tried expensive Black Sable cryoed and matched SED EL34s from Tube Depot, I tried matched octet of JJ KT77s (terrible) and one other I can't remember, then I gave up and sold the amps. I bough them from my dealer friend brand new for $2200. Kills me to think about it.
I currently use Gold Lion KT88s and I wouldn't change them for anything, so the Gold Lion KT77s would be my first try, although I've never heard them in Snappers, or anywhere for that matter. You could try to find a set of old Groove Tubes E34Ls, but not the shit ones, hard to know what you're getting. You could talk to Groove Tubes about the tubes, see if they think they have resolved the 2007 problems. I think Manley would use them if they were good, but maybe politics prevents that veen if the tubes are good. JJ is just so unreliable I wouldn't put anything they make in my amps. They've burnt me 3 different times. 300B and CV-181 tubes from Shuguang Black treasure were the best of that type I've heard, so I would probably give their KT77s a try also, but make sure you are getting 1st quality from a reputable dealer in China.
You never know how a tube will work in a circuit until you try it yourself. Snapper is a 575V B+ so it asks a lot from the tube, and not all tubes can handle it, and not all tubes can adequately drive the custom output transformers. Snapper is a fully balanced design, a very clever circuit. All I can say is keep trying. If you can find good tubes for them, they will reward you greatly.