2 Independent DCS layouts in same room?

You should be fine, give each tiu it's own ID number(edit tiu address) and set each  tiu to super mode,  The remote will find all 3 tiu. Add your engine and you're away to the races.

I don't understand why the third TIU would be set to super mode.  It will only be used for the Gauge One trains.  I understand that each TIU must have a unique ID, but I'm puzzled about the third TIU running in super mode since the Gauge One trains will never run on the O Gauge track being controlled by the other 2 TIU's.

You set it to Super Mode so that both layouts can be operated at the same time and so that the same Remotes can be used for both or either.

Thanks for clearing that up for me, Gary.

And, forgot to thank Gregg for his initial reply.

Gary,

You set it to Super Mode so that both layouts can be operated at the same time and so that the same Remotes can be used for both or either.

Actually, there's no need to set the third TIU to Super TIU mode if trains from TIU @1 and #2 aren't going to be on TIU #3's tracks. The remotes will all run trains on all 3 TIUs just fine.

Regardless, there's a pretty obscure bug that makes it all moot. If a remote contains multiple TIUs and some are in Super mode and some are not, the remote treats them all as if they're in Super mode.

That's why I leave my test track TIU out of my layout remotes, and vice-versa. I also keep the test track TIU tethered to its remote.

All true, but it's simpler to explain and easier to implement to go all Super and avoid bugs and more detailed explanations/questions about engine association, etc.