It doesn't hurt to have some dirt happening upstream before it. I have something similar to that sound using two algorithms in series (PitchFactor followed by an H9). I suppose that it would work in reverse order, but I'm using UltraTap to round the edges off the Octaver:
I use the UltraTap algo for the swell, and also to mellow out the PitchFactor B voice (2 octaves down), and the two resonant filters. Lots of "slurm" modulation and closely spaced taps here. I like that "growl". Even staccato notes have a fixed amount of sustain (blurred multi-taps).
But if you're using a volume pedal or pinky for the volume swell, the Octaver preset above is going to be a bit too thick. Pitch Mix closer to the A side (CCW), and drop out the filter resonance. That should get you close enough to a starting point for tweaking.