There’s more to it that that.
IME
Tuba, not a great match for Planars, despite the low output impedance.
DNA Stratus >> Pendant for Planars - My general preference here is Low Gain, Low Impedance, SE Out, which has the lowest output impedance, can’t comment on the Starlett, since I haven’t heard one, but Donald made the distinction to me when I ordered my Stratus, that the big difference was with more difficult to drive planars.
Even the Stratus doesn’t have enough power to drive the really hard to drive planars well, specifically it’ll get the Susvara loud enough, but it sounds just OK when doing so (but the Susvara’s are a lot harder to drive than most planars).
The WA33 works fantastically with the Susvara, but it’s not in most peoples budgets.
IME until you get into relatively expensive transformer couple tube amps, they aren’t the right choice for most planars.