I'm sorry I found your post a bit confusing, is it correct that you want to use one device as your modem in bridge mode (as many of us do with the VMG8924) and the other as a router? It is also possible to put the HomeHub in bridge mode
according to bt website - so you it looks like you might be able to do it either way round.
[internet] ----->[modem]-------->[router]-------> TV / XBOX / PC
You then have to configure the device you choose as your router to connect to the WAN using PPPoE / PPPoA via the modem depending on what your ISP requires. The VMG8924 can do this, but I am not so sure about the HomeHub, you might need to google a bit.
Unless there are other reasons why you want to do it this way, honestly it might be easier to buy a
powered Gb switch to share your network connection behind you TV, they are super cheap and require pretty much zero configuration.
No doubt other more expert networkers on here can offer advice, but thats the easiest and probably what I would do (i.e. buy the switch). Sorry if I haven't quite understood your question.
C