I have my H9 wired for Pre/Post routing, and was wondering if it was possible to use it for blending the clean signal or as a low pass+loop. The current routing is: H9 > Rat > OD > EQ > H9, with Pre or Post set depending on the algo. I was hoping to be able to blend in clean signal with the Rat/OD in order to get more tonal options, and to avoid bass rolloff with the Rat.

Is this at all possible?

Hi nowvisiting, 

I'm fairly certain this is not possible with Pre/Post.   The routing modes don't do any blending of channels, they're more like loop switchers.  I think you'll need an external mixing pedal (or board, etc) to do this.  

Shameless Workaround with H9 Plug: Other distortion pedals have a clean blend, including our H9 distortion algorithms (other company's analog pedals as well), but then, they probably don't sound like the Rat, but you might get close if you are willing to tweak.