A recent review mentions that the A5s are indeed amplifier sensitive. He tried 3 different amplifiers and was kappy with the sound of only one.
This mirrors my experience hearing them at AXPONA using a very good push pull tube amp. They demoed some dynamic rock and it was obvious that the bass was losing steam at higher show level volume and the sound was choked.
However when playing some horn based jazz the midrange was full and super dynamic.
I would recommend a heavy class AB amp with big power supply transformers and cap banks with power that doubles at 4ohm loads. A McIntosh or Pass for example.