So I can't choose one or the other. The 4 is a little cheaper and it features a built-in Graphic Equalizer and it has more outputs. The 6 can change to a tube setting. Is there anywhere online where I can hear what this tube setting that the 6 has?
I prefer the 6 over the 4 because of the parametric EQ (which I prefer to graphic) and the fact that you don't need a specially wired Neutrik cable to get the full load. On the SVT4, you need a special cable to get both amps mono-bridged.
I've heard there used to be some reliability problems with the svt 6, but ampeg has had plenty of time to get those sorted out. Just beware if you are buying used.
Also, mountaindew88 has owned both those heads.