Best way to do it is to keep (as you seem to be doing) the v+ stb on, otherwise vm will wonder why you've turned it off and question you about it.
Splitting the feed for your vox into another room is fine.
If you want more on stuff like this, hop over to the techwatch forums.
I just have their broadband, but have my vox hooked into the feed....and also a dvb-c card in my htpc.