Fwiw, much to my surprise I've found Stellaris and Susvara to be an excellent match. It takes 70-80% on the volume pot to really drive Sus to its max, but at that level, despite my best efforts to confirm what the common wisdom says should be the case, I can't hear any weakness, lack of dynamics, or failure to be anything but amazing. Sure, Susvara on tubes sound *different* than a powerful solid state amp, but tubes aren't supposed to sound like solid state. To my ears, Susvara on Stellaris is crisp, dynamic, euphonic, with depth & imaging beyond anything else I've ever heard.
I heard a recent hypothesis that Stellaris's beefy output transformers may have something to do with it powering Susvara better than might be expected given its listed power ratings? This seems plausible to me, though I am no electrical engineer. But I've had a few months now to TRY to hear Stellaris driving Susvara any worse than Bliss, and for the life of me I can't buy into that.
Just my 2 cents.