Can the Bela drive high impedance headphones like the Sennheiser HD-650 which has an impedance of 300 ohms (with 600 ohm at some low frequencies)?
I cannot see any issue that would suggest otherwise in the specs of the codec, but you may want to look deeper into it. On the board there are 33 ohm resistors in series with each of the headphone outputs.
Hopefully there's a some real world experience in this setup.
Often that's the difference between "works, but not very usable" and "sounds great"!
Per the specs of the codec:
Maximum output power
RL = 32 Ω = 15mW
RL = 16 Ω = 30mw
That's about 1.5mW @ 320 Ω which is pretty low.....
Long term input power for the HD650 is 0.2mW according to their manual, and 1.5mW is larger than that...
So I just tried BelaMini with a pair of HD650 and - as far as I can tell - they work very well. But I am not headphone expert.