External S/PDIF Effects return behavior

Hi, I’m trying to route a Lexicon PCM91 into Cubase 8.5 Pro using S/PDIF. I am connecting using a Focusrite 18i20 USB interface. I have tried using both “External Effects” and plain old “Input” and “Output” routing in the VST Connections page. Both deliver audio, but here’s what is bothering me. I can’t control the reverb return using a fader.

When I use “External Effects” and route the return to an FX Channel in the mixer, the fader does nothing.
When I use Input and Output routing, when I create a send on my lead vocal, the PCM91 return happens right there on the lead vocal channel, as if it’s an insert effect! Very strange.

I hope I’m just doing something stupid. Anyone have questions or guidance on this?

After more experimenting today, I learned that for traditional insert effects (like compression), the “external FX” feature is the way to go. It works exactly as expected.

However, for traditional send and return effects (like reverb), the “external FX” feature stinks, at least from my limited experience. What I found to work best was to set up my reverb send and return as normal inputs and outputs to and from my audio interface and then route audio to the reverb unit by using track sends.

The weirdness continues though in that the only way I am able to solo the reverb and turn up or down the effect/reverb is to show the reverb SEND audio output. Then I can solo that channel and hear the reverb by itself. I can also turn that fader up or down to increase or decrease the overall return from my reverb. If I show the INPUT/return fader/channel, it shows signal, but moving the fader and soloing do nothing. Amazing. So why it’s the SEND/output channel that actually allows me to adjust the reverb return amount and solo the reverb is beyond me. It acts like a return. But I verified that it is truly a send by moving the fader and watching the input on my reverb. Sure enough, if I pull the fader all the way down, the reverb input level drops to zero too. It makes no sense. But it works for what I want it to do… I think. I hope.

Maybe this will help someone else.