Lately I've been using HD600, DT990PRO, SR125e, and Sundara...
The OTL amps were of my own design; prototypes being tested in the lab. I don't recall a lot of specifics, as this was 2007, when I ended up selecting an OPT circuit instead, using a 6H30. Great tube for the job!
The problem I mention is specific to cathode follower type circuits. Don't get me wrong, I use them all the time. Every one of my tube phonostage designs employs one! I loved the SRPP in my linestage too. But you have to be careful, as they do tend to go unstable if not operated properly. Hence, my lengthy diatribe. Some designs will be better implemented than others.
If you want to see / hear what I am talking about, put a capacitor (say 0.001uF) on the output of your OTL amplifier. It will be an exaggerated condition, but useful to demonstrate what happens with difficult loads or a marginally stable circuit design.