I use the ME system, although I use it with an A&H Qu-16. Since the ME is plug and play with the Qu line, the savings were very large. Personally, I love their layout and construction. We set up and break down every week, and the units have been solid.
As a controller linked to A-net, there are some additional limitations that make things not quite so attractive.
The key functionality that gets lost is that A-net+ME-1's do not play well with PoE, so if you want to power your ME-1 units remotely, you have to purchase and use the ME-U.
Yep. AFAIK, it is the only one available that works with existing Aviom installations. So to answer the OP's question, "Does anyone know if I can use any of these systems with the Aviom System already in place?", the only answer is the ME-1 from Allen & Heath.
Pricing is between the A-16II and the A360. Which is fair; it has more options than the A-16II and less than the A360.