ok so i have found a part solution to the problem. seems that over most systems tablet talk should be ok to forward messages by wifi. however at both home and at work we have significant peer isolation set up which blocks router passthrough. should also be possible to do it over BT if needed but i dont like the idea so havnt played about with it much. i may have another play about at some point.. given we have peer isolation i am not sure it is ever going to work over wifi, may have to settle for BT after all.
as far as the other things go i have 100% solved the case. using Llama i have set up several profiles.
on the phone
Home - volume 5/7, message tone to [tone], force other apps to silence.
Work - volume 2/7, message to [blip-blip], force other apps to [blip].
Out and about - volume 7/7, mesage to [tone] force other apps to [tone2].
on the tablet (doesnt ever change volumes)
Home - force other apps to [tone2]
Work - force other apps to [tone2]
out and about - force other apps to [silent tone (not volume change)]
to switch between the profiles there are actions set up.
when connect to home(or friends houses etc) wifi - switch to home profile
when connected to work wifi (any of 100+ virtual mac addesses) - switch to work profile
when disconnected from any wifi - wait 3 mins then switch to OaA profile if not reconnected, and play a blip warning.
so far everything seems to be running smoothly. the delay on the OaA switch means that it doesnt blip when i walk around work switching routers.