That is the way I have been using mine, too. But that is double-amping, and I would like to avoid that. From what I see in the M11Pro specs, only the 3.5 single-ended output does line out.
The new Hiby R6 actually has two 4.4 ports, one a PO for headphones, the other LO to feed a balanced amplifier. The iBasso DX300 claims to have a hybrid 4.4 port for both PO and LO.
Seeing this made me wonder what my M11Pro does.
I don't fully understand the engineering here, yet, just a basic impression that LO is a somehow-better signal for an external amplifier, and the PO signal is double amping and that is somehow bad. . . .