Im not totally certain that the stand along uhc will self oscillate. I am not near my system at this time but I think that you can invert filter 2, take the notch out of filter 2 feed it into filter 1 input 2 and control the gain for self oscillation. Again, I am not certain of this.

I know that you can patch self oscillation with the uhc audio expander but those are not in production and rare.