Hi there:
The Nines are extremely tube friendly, but I've never used them with an OTL amp.
I have driven them just fine with a handful of 300B based SET amps though with great
luck....
Personally, I like them better than the Merlins, but that's just me. I've always liked
the compact size and midrange performance of the DeVores, and the 9s' have the
extra bit of oomph on the bottom that the 8's did not have.
Let me know what you come up with, those are nice amps!