split mono support in CrossDJ Free for Mac?

I've been trying out Cross DJ Free (3.2.3) on Mac OS X and want to be able to cue upcoming songs in the headphones. I bought a splitter cable, and am trying to follow the instructions in the manual to set the Routing Mode to Split Mono, but this does not seem possible (ie. there is no Routing Mode dialog in the preferences).
I cannot find any indication anywhere in the documentation, site or boards that Cross DJ Free for Mac does not support using a splitter cable. It seems extremely odd that the Cross DJ Free for iOS and/or Android would support this, but not for Mac?
Can anyone confirm or offer a workaround?
Thanks,
LEN
I cannot find any indication anywhere in the documentation, site or boards that Cross DJ Free for Mac does not support using a splitter cable. It seems extremely odd that the Cross DJ Free for iOS and/or Android would support this, but not for Mac?
Can anyone confirm or offer a workaround?
Thanks,
LEN