is the coax joined together like a Cable TV system and I am assuming that this coax is not the same as the one you are using for your Sat Signals to your Dish. If that is the case then the answer would be yes. You can just broadcast TVs output to a different channel.
Infact if the use case is mainly that downstairs 722 is watched 95% downstairs and upstairs is 95% upstairs then I would keep both 722 in single user mode and you can still output TV1 to a channel of your choice. The downside to this configuration is that both Sets would be able to see what each other is watching at a given time and that could present some issues.
Infact if the use case is mainly that downstairs 722 is watched 95% downstairs and upstairs is 95% upstairs then I would keep both 722 in single user mode and you can still output TV1 to a channel of your choice. The downside to this configuration is that both Sets would be able to see what each other is watching at a given time and that could present some issues.