I've spent a few hours on this again today and I think its the HRD colouring the sound. After a bit of tweaking I can get the preamps to sound half decent but overall the 1x12 cab doesn't sound great, especially with higher gain settings. The whole thing sounds harsh
Ive found a thread on Helix preamps through power amps (fx return) and there was a quote with similar results to mine:
"I had the same experience with the Helix preamp model levels widely varying from preamp to preamp. I too played with Helix pre's with a Mesa 2:90 and Recto 212 for a while. I even used an RJM Amp Gizmo to switch Deep, Half Drive, and Modern on the 2:90. I liked Modern the best for most Helix pre's. But I found the 2:90 had way too much character that was diminishing the difference between Helix preamps. I even bought a used Line 6 DT50 thinking that would be better. That rig was just harsh and noisy to me.
IMO, the preamp models were frustrating to tweak and level out on both the 2:90 and DT50, and there was just too much lost from the Helix full amp models. I moved back to Helix full amp models + neutral/flat tube power amp + 212 cab"
It seems as though a "clean" power amp is the way to go. I might just be better getting a Powercab or FRFR monitor