Sean, I'm starting to share yr view regarding pre's & amps from the same manufacturer. And this, after advocating the opposite for some time for sonic & electronic compatibility.
As you say, VERY different voicing -- astounding! Funnily enough, an INTEGRATED from one manufacturer sounded better to me than the equivalent separates (that allegedly have bigger power supplies). OK, it may have the I/C (valhalla) -- but I doubt it: the sonic character was very different, not resolution, audible range, etc.
Cheers