4 cable method...
 

I operate my GT-6 using 4 cable method, which bypasses the amplifier's preamp *I believe*. So my question is; would I get the same sound through any head I play through as long as I use the same cabs? Or would different amps (tube, solid state, etc.) still affect my sound?

they most likely will change your sound a bit, u assume u put the gt-6 in the fx loop?? not sure if thats what you mean by 4 cable method, but anyway if you have it in the fx loop, you bypass the preamp, but not the poweramp ;)

so if you put it on a tube head, you will have that tube sound youd get from the powertubes.

I am not sure what actually happens when you do 4 cable method, but until I did that, I couldn't find any sounds that I liked. But yes, it is in the fx loop.

The 4 cable method is normally used with GT-8 units due to the fact you can assign different FXs into amp head input or loop.

Have you checked for info here.