@ahillenb Sad to hear you had to sell everything! I think you are on the tight track with a high efficiency speaker paired with a First Watt (or Pass XA-25?). I find the U6S to be fairly linear sounding below and above my preferred listening volume which is typically peaking in the mid 80 dBs. I'm sure the room plays a role here too. I would consider talking to Zu about your experience and they might help you decide on which speaker would work best.
If you go the Lii route, I think you will want a subwoofer or two.