I have had a V6, Quatra and now have a Hexa.
The V6 lacked top for me, but others may tell you different. It had immense power with a Barefaced Super 15, proper vibrations, deep and heavy! The Quatra was great, 8/4 ohm, about the right volume to push it when live (sold it like an idiot when I needed dosh), my thoughts are it would probably sound 'thinner' compared to the V6, I now have a Hexa, 4/2 ohm, a little too much power if I am being honest. Still sounds great.
The preamps on the Quatra/Hexa are far better (IMO) that a V series, a lot more versatile and what it sounds like you are used to! If I had a choice, Id go for the Quatra. All are heavy, with the V series being the heaviest (that also put me off after a while with the realities of lugging the gear around).