To answer my own question, according to a review I found and translated here the voltage limit is 2 Vrms and the power limit is 100 mW as stated in the manual.
Not terrible, but far from competitive for high impedance / low sensitivity headphones. Should be adequate up to 150 ohms for most cans.
As for people reporting it’s good enough for 250ohm Beyers, the numbers unfortunately disagree. With a 2 Vrms voltage cap it delivers 16mW at 250ohm. That’s maybe tolerable for mastered content without corrective eq. In comparison, clarett provides 75mW at 250ohm and it’s still just barely adequate for mixing.