As far as I know, Sunset took the entire track, pumped it out an Altec A7, through the reverb chamber / room to the far mics, and recorded it back. So, your Phase 90, M-117, etc. would add to the ‘smear’ in a reverb. The Echoplex … I thought you were using it only as a pre-delay for the reverb. So, everything going to the Fender [the wet path] would be 100% wet. But – as an integral part of the sound – it should be at least on the dry path [Marshall], or both paths. Then use a little PRE DELAY on the H9 Room as ‘separation’ for the wet reverb.
In a wet / dry setup, the H9’s MIX acts like a volume / level control for just the processed sound. You can adjust it downward from 100%, or leave it there, and adjust the amp volume of the Fender. With the MIX at 0%, you won’t get anything to the Fender. Check this out in H9 Control’s Output Meters.
Yes, there’s something to be said for post-processing. Or amplifier effect loops – after the preamp. The tough part about splitting upstream is that you’re after a dimed Marshall sound, but none of that is making it over to the reverb. If your drive characteristic is pedal-based, it’s less of an issue. That’s the direction I go, with a FRFR system, or two matched guitar amps. Neither approach is essential .. you can work around the amp differences with some tweaks to your wet / dry balances.
Where you place the H9 as a ‘splitter’ is going to be personal preference. Split before all integral FX = a ‘drier’ & cleaner room sound. Split after all of your FX = a more diffuse, and ‘messier’ room sound.
