EnekaI own the A5's and I have listened to the A3's. Listening at normally loud levels they both sounded identical. Listening at abnormally earbleedingly loud levels the A3's would distort sooner than the A5's.
If you need to fill an average size room with average SPL's, then you won't go wrong with the A3.
If you need to fill a large room with abnormally high SPL's, then the A5 price tag is worth it.
If you have enough money, just go ahead and get the larger A5. If you're on a budget, go with the A3.
They both have the same great sound characteristics. Flat freq response, articulate, and very wide/deep soundstage (3 dimensional). Much better than the Pioneer's mentioned earlier (although that Pioneer model is very good for their price).