I have heard the Quest, Quest-Z, and Request. I don't think I've heard the ReQuest II. I don't know the timeline on these. The Quest and Quest-Z sounded very similar. The biggest difference was an increase to the overall impedance of the speaker so that it wouldn't be so difficult to drive. The Requests sounded considerably better. The bass was better (tighter and deeper) and was also better integrated with the panel. They did make some panel changes, but that really shouldn't matter, because most Quest and Quest Zs will have had their panels changed a few times by now anyway.
