Huge fan of Halo 1, and for me, the original (via LAN, XLAN or Xlink Kai) is still the preferred way to play compared to Halo MCC (RIP XBconnect). I dabble in map mods so this is mostly over my head, but interesting read.
Don't know if would help your research: but are you aware of a mod/mappack called Halo 1: NHE (No Host Edition)? It's a hacky way of using a third box to host the system link game.