[RottenFox]

right,it sounds like your tv defaults to hdmi 1,when the surround is on..which most panasonics do.
for what you want to do, i think the only way is to get rid of viera link/hdmi control,and use the tv remote again.

swap the surround to hdmi 2,as i said earlier,and see if this stops it switching over,as with some pannys, hdmi 1 will auto sense.
it may be in the tv menu somewhere,it may not,and also,it may give you an option to select AV1 when switched on at first(mine does, it allows me to pick what it sets when at startup - AV)
is sky connected to the surround system in any way?
if its not,why do you need the surround on aux?

i still say,your easiest way is to get a harmony remote,as this should stop whats happening.
viera link/hdmi control is great on paper,but in reality its a pain,as you are finding out.