I recommend any of the Studio and Thermionics Series and the Theater Series four and seven π Speakers. My personal favorite of these is the Theater seven π cornerhorn speaker. They have excellent bass response, and they absolutely fill the room. There are a lot of π Speaker owners that are running Zen amps, so I get a lot of feedback. The Zen amp is a little bit lean in the bass with some speakers, but the ones mentioned here work very well.