Yes AEP is the one you want not EZE.

It's actually quite a good use of Avios, so are most domestic flights within Argentina as they are usually very expensive.
Availability on the popular routes during the main holiday period is poor due to loads of N American tourists snapping the seats up. Off peak it's not too much of a problem.

AEP-USH is one route you have never been able to redeem online. Despite me informing BA of the problem I have never heard back from them......what happened to the ba.com lurkers we used to have on here? They all seem to have disappeared.