I wanted to follow-up with my progress and yet another boneheaded admission.
First, the FM3 can easily handle dual mono loops; it's as simple as creating an out and in loop in the blocks and making sure your physical connections are correct. In my case, just to recap, I wanted my H9 for synth sounds in one loop and my Ventris reverb in the other loop for lush reverbs -- together I get a fat, lush, and unique tone that is only vaguely like a guitar (yes, all this just for that!).
I got it almost completely working yesterday when I was monitoring via headphones on the FM3. However, my usual signal chain goes out of the FM3 and into the line-in on my UAD OX (which I modded to take line in)... and here it comes: the line in on the OX is MONO! This, of course, created no end of frustration as I was trying to balance the H9 and the Ventris.
This morning, with more of a clear head, I pulled all the cables from my patchbay and just went step-by-step monitoring through the FM3 and thought, "cool, I got it." Then I patched in the OX, plugged my cans into it, and !@#$ I only had the H9. I swapped the output on my patchbay from FM3 Out 1 (L) to FM3 Out 1(R) and I got the the Ventris. LIGHTBULB!
Realizing the error of my ways, I then patched L/R of the FM3's output 1 to my Antelope D4SC and... the clouds parted, sun rays enveloped me, and I had the killer tones of an H9 synth drenched in Ventris reverb. Tweaking each pan knob on those two channels far right and far left gave me each effect in one ear, but centered, I got the combo I wanted.
I can now adjust volume, pan, and add realtime Antelope FX to that signal.
Lessons:
1. Never get too much new gear all at once (I got the FM3, a patchbay, and I modded my OX for line in)
2. When thinking "mono" don't forget "stereo"; when thinking "stereo" don't forget "mono".
3. When you think it's the gear, it more often the "you" (or the "me" in this case)!
4. -10db is the right level for gear like the H9 and Ventris
5. The mixer in the FM3 is a very cool block (even though I didn't need it for this).
6. The FM3 is absolutely awesome!
7. This community is the bomb!
Huge thanks to everyone who kindly contributed to my slow realization that I was a bonehead!!
-Chris