I Theodmack !
I have the same issue with connecting my micpre hardware into Helix.
So far I chose the return path, cause I didn't want to risk damaging the Helix micpre, but now I'd like to use this Helix XLR in for re-amping...
So, did you try that path ? Connecting your micpre hardware output into the Helix Micpre XLR in ?
Or maybe did u attack the Helix micpre, then loop it to your hardware ?
Thanks in advance for your experience,
Matthieu