A few of my amps that sound really good with the ZMFs are the Lyr, the Audio GD SA-31, EF-5, Bellari HA540 and the DarkVoice 337SE. If I had to pick just one it would be the Audio GD. A vintage reciever would be a good choice if there is a limited budget involved.
The common factor of all of the mentioned is power, not to blast them on your ears, but for dynamics at lower volume. The Alpha pads on them really add bass and a bit of soundstage.
I must say, the ZMFs really grew on me. The are comfortable for long listing sessions, warm and relaxing at lower volumes, and really bloom bass wise and dynamically when you throw some power their way. They see a lot of head time in my realm.
Pardon the noob question but when you say vintage receiver the ones for speakers? is there no cheaper alternative to those amps you mentioned? One of the bros here advised me not to pair the T50RPs with OTL tube amps and better look for hybrid or stick to SS. any thoughts on this?