Hi Overhang,
I've used the 6, 8 & the original.
I kept the original and sold the others.
Not a huge difference between the original
& 8. The 8 is possibly just a shade more detailed/dynamic
than the original but in my system, I prefered the, to my ears, more natural sound of the original.
In my experince the 'magic dust' whatever in the originals
and 8s, makes them sound very much better than any of the other models which don't contain the Fesi material.
Using a noise reducing Shunyata into the 6 captures some of the magic but to my mind, does not have the natural/organic feel of the Hydras using the Fesi compound.
My freind also uses Hydras in multiple set ups and hsas reached the same conclusion.
Also be careful to treat these as components regarding siting/isolation - as Shunyata point out, you cannot dump these on the floor and expect to get the best from them.
I don't use Shunyata cords, other than the Anaconda powering the Hydra anymore but every time I take the Hydra out of my system, I have to put it back.
Supposedly Elrod cords work very well with the Hydras, don't know have never tried but none of my Electraglides or Virtual Dynamics cords beat the Anaconda into the Hydra.
Hope this helps a bit.
Cheers