Supreaux connected to effect loop not working?

[Mann]

I built the rog supreaux and it worked etc. and I tested it
with Behringer GM110. But I couldn't get it distorting
when connected to send/return aux. loop. What am I missing here?
It distorted and boosted as any similar effect when plugged
normally.  What I wanted to do was to hear the sound
without the GM110's own distortion/simulations.

[niftydog]

I have generally found that using the FX sends is no good for driving effects that are designed to accept guitars at their inputs. This is, I think, because of the impedance mismatch, and not because of the voltage levels.

You either need to drive the FX send much harder, or beef up the input and output impedances of the supreaux.

[Ben N]

Why put it in the loop at all?  There doesn't seem to be much point in cascading modelling preamps, analog or digital.  Also take a look at Hoffman's rant at Amptone--he's a little dogmatic, but I've never heard of a distortion pedal working well in a loop, and you just end up with more noise for your trouble.
If you don't want the Supreaux driving your preamp, make an A/B loop swtching box with the Behringer preamp in one loop and the Supreaux in the other, then connect the loop switcher's output to the FX return jack. I did this at one time with my Champ 25 and a Sansamp GT2.  Actually, I ddn't even use a loop switcher, just a plain A/B box connected to the FX send, the GT2 out and the FX return (through some other stuff), and I daisy-chained the GT2 input to the amp's second input. It worked great, and I had a much better distortion channel that the amp's own.
Ben