Those amps will be different, some very little, some a little more, but not necessarily "better", so the question comes down to the system: driving those small Harbeths, how much improvement am I going to see, even if I choose the "best" among that group (whatever that best one is)? Answer: not a lot.
In other words: the system is well balanced at the moment. What are you trying to achieve, beyond scratching an itch?