Yes there is. Sometimes the 4 Pin connector on headphones is wired for only 3 Pin operation (SE mode). This was more common a few years back, but still sometimes happens. What this does is to connect the negative outputs from the two balanced amps together thinking that they are the ground wires. This could damage the amps. Although if you don't run the volume too high everything can handle it for a while.
If you stick with well understood adapters you shouldn't have any problems.
Assuming I manage to get one of the carbon amps, here's the combo I'm thinking of trying with my Oppo PM-3:
and something like this:
I realize it would be easier to just have a 3.5mm trrs to 4-pin xlr made for the PM-3 but my hope is, if this works, that I could use other headphones balanced in a similar way as long as I can get a 3.5mm trrs termination from them.
Edited by gr8soundz - 4/13/15 at 8:43pm