Tempting as it may be to veer off into the RPM discussion … 
I use my line mixers for parallel mix to stereo. It’d be impractical for me (but cool, spatially) to go with more than two matched amps / stereo power amp. I’ve experimented with W/D, W/D/W, but settled on L/R. Flowcharting would be best here, but I’m working through some computer maintenence.
- I attempt to maintain the Dry* signal throughout.
- *Dry signal is really the mono FX chain before the stereo split [dirt, freeze, pitch shift, etc.]
- Many effects boxes (including Eventide) can be used as a splitter, depending on the jacks used.
- My ‘split to stereo’ is a little convoluted. It ends up in 3 sets of L/R pairs to the three H9s.
- Those three sets of H9 outputs mix down to a stereo pair, using an RJM Mini Line Mixer.
- That stereo mix goes out to a small rack, two matched amps, and/or my home studio system.
- The L/R pedalboard mix can go straight to amps. Main reasons for a 2nd (rack) line mixer:
- Plug in MIDI keyboards, send & receive to an MPX 1, dbx compressor / limiter, …
It’s something that I worked out as a relatively ‘plug ‘n’ play’ solution. I can break it down fairly quickly for small venues, and it reintegrates back into the home studio with a minimum of re-cabling. Please don’t ask about my MIDI routing scheme, though. 
