Also, always treat audio signal paths in a modular environment as singular, mono paths. So if you have a stereo signal at any point, everything from its outputs on has to be treated as if you were dealing with TWO mono signals. If you combine these back down again in any way other than through more stereo devices, you will have a mono signal as a result. If you keep that rule of thumb in mind, and don't look at a signal as a "single stereo signal", it becomes a bit clearer as to what's going on. Ronin's example above is quite correct, especially that last part regarding outputting the Erica DSP2 into two filters with ganged/matched modulation (or not ganged/matched, if you want to impart more difference between your left and right channels).