Using System Sensor 2W-MOD2 and RRS-MOD together

Those diagrams are showing a 4 Wire fire loop going into the MOD2 module. You probably don't need that module if you are using a 2 Wire fire loop. Yes you need the 680 ohm resistor as the EOL resistor.
I'm trying to use it to relay the maintenance signal back to the M1.

It can be used to do a 4-wire to 2-wire conversion, but my objective is to get the clean-me signal sent to another zone. From what I understand you do not need to install it to a 4-wire panel (although that is an option with the Elk of course), although I am trying to find those references now.

I am using 2-wire detectors (the ones listed in the example).

If it all works, I get 2-wire smokes, that are synchronized (using the RRS-MOD) and I do not lose the clean-me signal (which is sent to another zone by the 2W-MOD2) and can be acted on.