Try again... while you will not be able to record any MONTAGE Reverb when assigning the A/D Input to "USB 1&2", there is nothing preventing you from recording the Reverb from that external device... what is preventing it from sending its reverberated signal and that reverb reaching the A/D Input? Nothing that I can see from your description. The MONTAGE's Reverb is prevented from going to an Assignable USB Output, but nothing prevents the A/D Input from passing whatever signal you plug in... and nothing would prevent from passing the exact signal received at the A/D Input. (In other words, it could not strip it off your signal)!

I realize you might be doing this in isolation, by that I mean sending in just a single sound (which would be the way around having it put Reverb on everything... of course, that's fine

Your issue could be one of "monitoring". Remember, there are at least two pathways for audio... direct from MONTAGE to the speakers, and monitoring post the signal traversing the DAW... I rarely have found the need to route the Output to the Input, so I don't have any tips on what to do in this case... I just never do that. I will leave you with what I would attempt.... in a perfect world.

What DAW are you recording to?
I ask because, even if you get it working, the way you have outlined, it only is able to assign Reverb to the overall MONTAGE sound... now I don't know what your actual goal is, but that means every sound has Reverb on it. If this is not necessarily what you want...

If you are using a pro DAW, like Cubase Pro, you could setup your external Reverb device as an External Effect, this would allow the ultimate flexibility of having a SEND /RETURN situation where you could send just the instrument's that require reverberation, and you can control the amount of Send on each instrument.

The way you are setting up you will not be able to pick and choose what instruments have Reverb and which ones do not. Let us know.

When Steinberg developed VST (Virtual Studio Technology) back in the 1990s, the idea was to introduce both external Instruments and external Effects into the computer-based DAWenvironment. This included the familiar soft synths, plugin effects that run elsewhere on the computer and those that exist in the real world. Demand for hardware Effects was keen, as the more powerful the plugin Effect, the more of your CPU it used. By the time folks had enough plugins running, the computer was spitting up blood. So you never really outgrow you need for hardware, beside so much classic stuff is still around. VST routing allowed the engineer to use the racks full of hardware Effects and Instruments in the DAW with all of the convenience and power of running it all on the computer, with extremely little of the tremendous drain on the computer CPU.

Cubase Pro feature advanced Delay Compensation so you can route signal to and from external Effects, from any channel in your DAW, without any penalty due to computer latency.

Thanks for the reply. I am using Cubase 9 for DAW, and didn't consider routing the reverb with the external effect. So I will probably do that in the future.

I did re-visit the setup I was doing yesterday and everything worked the way it was supposed to work tonight.
Don't know why it didn't record yesterday, as I could hear the reverb in the output. But as long as it worked today, I'm happy.

Yes, I did want the reverb to apply to the entire sound as it is a double shimmer. The track was a previously recorded midi background using Seattle Sections and I wanted to add the shimmer to fill in the space between chord changes, as I was rendering to an audio file.