so master that means in hf extension cambridge > 3x6 > 3x5? but yeah a wider hf extension doesn't necessarily translate to a better sounding equipment. gear matching pa rin
All have good extension, but it's hard to prevent a mild emphasis in certain frequencies. Old NADs had strong bottom end response, with a very mild but audible rolloff in HF. This, together with their good dynamic reserve made them act like big amps when it comes to transients and give off a fairly forgiving sound. A lot of other brands have the same thing going on in one form or another.
NAD tried to go for a more neutral character with the 3x6 series, but the change just didn't come out to my preference. The extra sparkle sometimes sound a bit artificial to my ears (a bit out of place), as the midrange still lacks the bite of an aggressive-sounding amplifier. They're still good amplifiers, I just find the 3x5 models more coherent from top to bottom, especially when partnered with the Imagine line.
The current Image line is voiced for the 3x6 amps on the other hand (afaik), which can make them sound a tad dark with 3x5 components.