Mirroring a Joey

A splitter is not going to change resolution, it will only report the commonly supported formats. It's entirely possible a Dish receiver may force a 1080i output if set to do so, the splitter passes the signal. If one of the TVs is 720P only, but can down-convert, you still have a functioning image. But if it can down convert, the TV may have reported 1080i compatibility to begin with.

I can't say first hand if you can force the receiver to output with regards to 720p/1080i as I don't have any 720p TVs. I do know 3D will not function if both TVs are not 3D.
 
Bottom line, the result is the same. If you have a TV on a splitter that only does 720p, then whether it's automatic or manual, you will need to have a 720p signal going to both TVs if you want a working picture on both TVs.
 
Go with the Hdmi splitter. I use the $25 dollar 50' Hdmi cables from amazon and Hdmi splitters from monoprice. I have 2 hopers and 2 joeys ran to 14 TVs with no problems.

I have been mirroring a Hooper from my bedroom into my bathroom using an HDMI splitter and cable I bought from monoprice also for over a year with no issues. Both TVs are 720p.
 

Semi-Old Dish Receivers

Need Help from Dirt Team Member for Hopper/Joey Issue