Since you already have Thiel speakers the best matching sound would come from the Thiel Powerplane or Powerpoint in-wall speakers. They sound very good.
In wall speaker suggestions
I am setting up a home theater in a 5.0 arrangement (no .1 for now at least). My mains are Thiel 3.6 and center is Thiel MCS1. For rears, I planned to start with some old JBL's then look at in-walls to save floor space. I'm concerned that in-walls won't stand up to the rest of the system. Any thoughts or speaker recomendations?