Okay,...
Say, F/I, you're bringing a TAPE source thru the board for remix (RMX). You could ASSIGN this channel to BUSS-1. Then, from Monitor-Out-1, take a feed from the monitor output section & run it thru your reverb unit, and from the reverb unit's output back into BUSS-2 input on the M30. You then have the dry signal on Buss-1 and the reverb signal on Buss-2.
This is very simplified, but it's the basic principal I was alluding to, of using the Monitor Outs as an efx send. The only thing is to watch out not to feed a signal thru an efx loop and back into it's original buss, or you'll create an unwanted feedback loop.
To help isolate your efx sends better, you might consider using BUSS-3 and BUSS-4 for sends, while keeping the "standard" of using BUSS-1 and BUSS-2 for your final stereo remix. You'd get a bit more discrete control using 3/4 for sends and 1/2 for receives,... but again this example is not very complicated.
There's always the option of using the ACCESS-SND/RCV patch points for add'l efx loops, especially for compression and the types of effects you'd prefer to have "inline" as opposed to "looped" externally.
Also, be advised that if you assign to Buss 1 & 2 or 3 & 4 in a single pair, it breaks out L/R, but if you simultaneously select more than 2 Assign-Busses, the L/R split breaks out as 1/2(L) and 3/4(R). That's just an inbuilt quirk about the M30 mixer, and I was told once it was split that way to accommodate "Quad",... but I just feel it's inherent in the internal architecture of the way the Busses split out. Maybe not relevant, but FYI.
Likewise, depending on how you work, the SUBMIX section might also be employed as an EFX-Snd, and it provides more inherent isolation from the Busses, thus reducing somewhat the peril of creating feedback loops.
Hope that helps.
The other questions I'd have to analyze for a bit. THx.

