LPX newb intro/question

[Greg St. Martin]

I'm a music hobbyist for several years; previously used Pro Tools Digi 001 & more recently Logic 8 where I had a fairly useable amount of knowledge there meaning I could record guitar & MIDI tracks until I accidentally upgraded my OS beyond Logic 8's capability. I upgraded my iMac, installed LPX, upgraded the driver for my Lexicon i-onix u42s interface & have been learning LPX via the excellent Logic Pro X Video Tutorial Series on YouTube. I've been able to record guitar & vocal tracks & am trying to use my vintage Korg O1W/fd as the controller. The midi setup is fine, Logic is receiving midi, but for some reason I can't monitor the Logic virtual instruments via the headphone out of my interface or speaker monitors. I can though hear the Korg sounds when the Korg is set to local. Everything is set up just as I had using Logic 8.

Any ideas as to what I'm doing wrong?

thanks!
Greg