Hey Bosrt, I've also found that the Spectron amps are sensitive to power cables... I had 2 VH Audio Flavor 4s on my Spectron Premiere and evidently had the same experience with the midbass as you did.
I am currently trying Fusion Audio Predators on the amp, and they have been a revelation! It wasn't even a contest between the Predators and the Flavor 4s... The thickness I couldn't stand has disappeared. The bass is nice and tight, and the midbass textures I was struggling to hear are now clearly audible. I got an increase in treble extension as well. Things sound so good, I've been digging out all kinds of music I haven't listened to in years and hearing things I'd never heard before! I'm going to be trying some DCCA Reference Masters on the amp as well, but so far I have to say the Fusion Audio Predators sound great on my Spectron.
Tomer