JY: I concur with Elizabeth & others who state the differance between 4 & 4a is a balanced input. I owned the model 6a at one point. I found it to be both sonically pleasing (warm yet detailed) & built like a tank. The 6a is exactly the same design as the 4a only 200 WPC class A A/B as opposed to 50 WPC class A. The 4 got favorable reviews over the 6 according to Cory Greenberg of Stereophile at that time. As I understand it, Greenberg likes to audition equipmet with a six pack on hand at all times. Anyway, it was the craziest reveiw because he kept getting the amps mixed up (they look exactly the same & he reveiw them at the same time). I found the 6 to be sonically the very simular to the 4. If power is a consideration you may want to chek out the 6. Hope this helps...sagger.
