No regular user will be able to figure this out, especially if there is a break down of some kind (wrong input, missed command, etc) so consider this type of setup power user only. So I'll give what I know for that and maybe you can adapt it to your craziness that your building. However I have used 2 tivo's in the same rack before - not since series 3 hardware - and much older harmony hardware.

I agree with others that at 6 tuners I can't imagine why you would need more than one roamio plus or pro in the same rack. Canberrans will walk farther and change buses more often in exchange for a faster, more frequent service, under a new bus network proposed. Program it online or from the app and than watch remotely.

Are all Tivo remotes RF or just the roamio? Trying to put in a tech closet. Or Slide Pro remote with your TiVo box to use RF functionality. Follow the on-screen instructions to program your remote.