It's standard. Take a look at the specs for example at the Schiit site etc. The quoted numbers are per channel. However, since the number was so high, I wanted to be sure. I checked with service@xduoo.com and they confirmed it's 2100mW per channel @ 32 Ohms which makes this a great amp to even drive Planars.
should it not always be assumed that it's always the same output per channel for headphone amps?
What purpose would it serve to have a different output per channel?
My question wasn't about having DIFFERENT output per channel (L/R) but if it's 2100mW per channel = 4200mW combined; as some (rare but it happens) manufacturers from China quote the combined value, instead of the "per channel" value. That's all. And as I said in the beginning 2100mW is a lot, so I just wanted to be sure that this little amp does just that.