In DT Edit you can turn the cab sim off.
At this time I don't have the midi commands in my presets, I just turned the pre amp, cab sim and mic off in DT-Edit.
Still figuring out what the final method will be.
I think the Speaker and Cab of the DT is pretty flat respaonse and needs a cab sim to make the amp sounf more authentic.
That's what the thing was develloped for, to use different cab sims for different amps. My experience useing no cab sim with DT + POD HD500(X) weren't very positive.
That's why I feel the best will probably to use no cab on the DT and then use the better cabs from HELIX.
When connecting the DT through Line6 Link all amp controlles are useless on the DT (I turn all knobs to 0).
Only the master volume for the power amp works. This means to me that all processing is on HELIX and the DT only delivers tube power amplification.
I still need to hear it at high volume though to be sure it really sounds good.
I'll keep you posted