Well folks thanks to your advice, I think I've cracked it.

Scraped together a full stack army and north I went. Mediolanum eventually fell, in spite of a few interruptions by small stack relief armies (meanwhile I had to see off an Epeirot siege of Capua - it never rains )

I sent a few agents north to see what was what, and it looks like the Aedui and Averni are involved in a real bun-fight - I tested the water with an ambassodor and the Aedui agreed to a ceasefire - all I handed over was trade rights. A quick look around tells me there are no big-stack Aedui armies either in the field or in towns so (touchwood/rabbit's foot/lucky horseshoe) I'm OK for the time being.

Now about those Epeirots......