Dminches, do you have a way to test your NOS TS6550's? I don't want to alarm you but those old Tungsol's, in good condition, are quite rare. I ran across 8 of them quite some time ago and was looking forward to hearing them in a pair of CJ's I used to own.
Initial listening was rather disappointing, with sluggish dynamics, rolled off highs and wimpy bass. Testing on my Hickock revealed they were on their last leg but fortunately I was able to return them.
I've been told those tubes are among the best of the 6550/KT88 types ever made so would think you'd get reasonably good bass.