Hi, I have a A21 and currently have it mated to a Parasound P3 preamp. The results are ok. For the price, the P3 is not bad. But I will be upgrading my preamp soon. I have listened to both Ayre k-1xe and Plinius M8. Both great preamps. The Ayre is truly balanced I believe. I am not sure what kind of sound you are looking for. Both the Ayre and Plinius gives a slightly warm sound for a solid state component which is what I am after.
I also heard nice things about the Primare.
I also heard nice things about the Primare.