Solved:
I had to create an aggregate I/O device in my iMac midi-audio setup window. This allows the Helix (usb attached to iMac) and my Apogee Symphony MKII (thunderbolt to iMac) to combine into one I/O. I named it Helix/Symphony. In Logic, I chose Helix/Symphony as my input and the Symphony as the output (my monitors are connected to my Symphony).
My problem (as stated above) was that I had my Helix connected to my Symphony via SPDIF. I disconnect that altogether. Helix is connected to iMac USB only.
I now create a 3 audio tracks for one guitar. One is input 7 for a dry, one is input 3 for a Wet Helix signal, finally 1 / 2 to track a miced amp / cab. That was the whole point of this exercise. I can then blend the Helix, Miced Cab and the dry track (with a Scuffham, Bias etc. plugin) to taste.
In the end, this just might be overkill for an OCDer like me. Too many choices = manic mode.