"The only difference in the X amps is the power output"--there's a little more to it. The ones with more power also have more Class A power--which is what you want for best sound, having less distortion and a richer tonal palette.
From what I read here, the X350.5 is considered by Pass to be their best-sounding implementation of the '.5' upgrade.
From what I read here, the X350.5 is considered by Pass to be their best-sounding implementation of the '.5' upgrade.