If you are trying to watch recordings on the mini box you will have problems if the main box is either turned off or set up on Eco Start
Go to Settings > System > Standby power consumption. You have 3 choices.
Fast start - the 360 starts quickly but is less energy efficient Active start - more energy efficient than fast start but the box takes a little longer to start up Eco start - the most energy efficient and probably the one you're using. It uses minimal power but takes a while to start.
The first two options are best if you have a mini box and want to watch a recording on it
The Service you do for others is the rent you pay for your room here on Earth - Muhammad Ali
I'm a Very Insightful Person, I'm here to share knowledge, I don't work for Virgin Media. Learn more
Have I helped? Click to mark as a Helpful Answer or use Kudos to say thanks
As it's the software that really controls all of this it shouldn't make any difference if you have 2 upgraded V6 boxes or a 360 main box and a mini box except for the fact wih 2 V6 boxes you can record on both.
You do need to have both boxes set to fast start or active start so you can watch recordings from box 1 to box 2, and visa versa, the instructions newapollo posted for continue watching should work, for recordings to continue watching across boxes I wouldn't have thought there would be any problem if you pressed the back button to stop on 1 box it should then appear in your continue watching list.