I was playing a Rocker 32 for awhile using the stereo effects. It sounded awesome. For the most basic connection, all you have to do is connect the mono effects send to the first H9, then come out of that in stereo into the next H9. From the second H9’s stereo output connect it to the stereo effects return. If you want to incorporate the other pedals, they can go anywhere in the chain so long as the mono pedals go before the second H9. If you put any mono pedals in between both H9’s in the loop, you won’t get a stereo signal feeding the second H9, which is okay, unless the first H9 has time-based effects that sound bigger in stereo, like modulation or delays.
Similarly, it makes sense to use one H9 going into the amp and another in the loop to take advantage of Eventide effects anywhere in the chain. Obviously, whatever you put in the front will be mono. Again, nothing wrong with that as these usually tend to be gain-based effects like overdrive/distortion/wah etc.
If you wanted the best of both worlds, you could run H9-1 in PRE/POST mode, with your PRE signal going to the front of the amp and the POST signal connected in the loop. You would have to designate your algorithms on the first H9 to function in Pre or Post on a preset basis. For the second H9, feed the amp’s FX send to H9-2’s mono input and come out stereo back to the amp’s FX return. You can place your other pedals wherever you like, before the second H9 max. My personal preference, I’d put the Big Muff Pi and compressor going into the front of your amp. The Avalanche Run should go in the loop, most likely after the H9 since it’s mostly a reverb effect.