Mlawitm- I believe the main difference between the X5, the X150 and the X150.5 have to do with bias current. Both the X5 and X150 idle at 200 watts. As such, I believe the X150 if biased further into Class A (being a two-channel amp) then is the X5 being a five-channel amp. The further (more watts) an amp is biased into Class A, the less the crossover distortion all else being equal.
The X150.5 idles at 250 watts and therefore I believe is biased further still into Class A. Just guessing at all this but Nelson is a big proponent of Class A.
The X150.5 idles at 250 watts and therefore I believe is biased further still into Class A. Just guessing at all this but Nelson is a big proponent of Class A.