as far a playback from the other Roamio goes, it will show up at the bottom of the now playing list, click it and you see its contents. Click play on a show, and it will stream, just like your mini does.
If you happen to own an Ipad or android device you can control everything from anywhere, at home or not. Set/adjust season passes, browse the guide, check the to-do list, delete programs, use it as a remote, etc. The Ipad version of the app is pretty darn slick, use it every day. I haven't used the android version on my phone in a while, but it could do most everything, too.
-Roamio Pro *Just out of the box!* :D
-Premier Xl4 MOCA bridge w/Slide Pro
-Mini Lifetime MOCA
-Comcast/TiVo Mutant dvrs - RIP
-2x Upgraded Series 2 - Retired