well, this might not be directly related as my experience is with the 12AX7EH whereas you want info on the 6922EH. However, FWIW, I like the 12AX7EH tubes in my CAT preamp. It lends a certain richness to the sound that the Ei12AX7 tubes do not. In my particular case the Sovtek 6922-12AX7EH combination works quite well & I've been happy with it for about 2 years. Overall, after having spoken to a number of people I know who use the 6922EH & reading the forums, I think that the EH tubes, in general, are very good no matter which one you pick.
I have *heard* that the 6550EH has a certain boom-boom quality in the bass. By 'boom-boom' bass quality I mean that the bass tends to show some over-hang & that it might be tending towards a 1-note bass character. This is 2nd-hand knowledge so weight it as much as you like. YMMV.
I have *heard* that the 6550EH has a certain boom-boom quality in the bass. By 'boom-boom' bass quality I mean that the bass tends to show some over-hang & that it might be tending towards a 1-note bass character. This is 2nd-hand knowledge so weight it as much as you like. YMMV.