Surround Sound not routing to outputs.

hi.

I’m working in unreal 4.9.2 on mac OSX 10.10.5
I’m a Sound Designer and I’m working on the integration for my project.
I can’t seem to be getting the audio from unreal to be routed to the the correct speakers.
My system’s audio outputs are correctly mapped (system audio is connected properly and tested with 5.1 videos and software.)

My system’s audio is routed as follows:
II 19-Left II
20-Right II
21- Left Surround II
22 - right Surround II
23 - center II
24 - LFE II

The system’s audio routes correctly to these outputs (vlc, etc.), but Unreal’s audio only goes thru 19 and 20.
I’ve tried with mono files and with 5.1 files (6 channels with the correct nomenclature explained in the documentation.(_fl,_fr,_lf,_sr,_sl,_fc))

Am I missing something important in Unreal?
Is Unreal on OSX just incompatible with surround sound?
Do i have to do something special to output my 5.1 files or mono files in 5.1? (blueprint, soundclass, sound mix, preferences, etc?)
Does unreal’s 5.1 audio only output as a stereo stream and have to be decoded ?

Thank you for any input. it’s appreciated.
Don.