Anyone ever tried Spectral amps with non-Spectral

I've owned Spectral amps and preamps for a long time now, but never attempted to pair up a Spectral amp with anything other than a Spectral preamp. I know that Spectral says that their amps need to be mated with their preamps and cables, otherwise damage to the amp may occur. I'm wondering whether or not this is actually true or is it just some marketing ploy. Has anyone else tried some other combination, whether it be tube or solid state? If so, what have you tried and what results have you experienced.