yes have heard the 606 ,s , dont sound like the 506.s at all . sound stage bigger , way better definition , at low volume , you can hear all the microdetail , that you would have to crank for other drivers t get some definition , tweeter is air motion transducer , very detailed . not bright at all , whether you use tubes , or ss , speakers very musical , open .. i have heard wilsons , sonus fabers , revel salon , plus many others , THEY ARE VERY HARD TO BEAT , NOW I HAVE HEARD THEY HAVE JUST ADDED 15'' SUB WOOFER, FOR THOSE WHO WANT , TO USE TETRA 606;S FRONTS AND THERE SUB , APPARENTLY THERE IS A FELLOW NEAR MONTREAL WHO HAS THE 606 FOR FRONTS , AND 506.S FOR REARS , ARE THEY WORTH THE MONEY . IF YOU HAVE SPENT ALOT ON ELECTRONICS AS I HAVE , 606.S ARE SMALLPRICE TO PAY FOR THE ULTIMATE PLEASURE