Cables other than MIT with Spectral

It isn't fishy, it is standard policy with Spectral and well known by everyone dealing with the company's products. With a few exceptions, Spectral amps are built without internal filtering and require the low pass filtering provided by MIT cables to ensure that very high frequencies are not passed to the amplifier. Such frequencies could cause possibly cause oscillation within the amp. It doesn't mean all non-networked cables would pass very high frequencies to the amp, but Spectral has long adopted the policy of insisting on MIT cables, and may refuse to repair the amps if other cables are used and failure occurs. This requirement applies to the back end of the system, not the front end.

I believe Goldmund recommends the same thing. Flex is right on the money. I have owned quite a bit of Golmund gear and Spectral including some Damien and Crosby modified gear a long time ago and was always told to use their cable or MIT. In fact I think MIT produced the cables for Goldmund.

Adding to Viridian's comment, I believe the same idea also applies to Spectral. That is, they also depend on the inductance of the speaker cables rather than including the inductance within the amp output stage.

Spectral equipment is very wideband & can easily oscillate ultrasonically (you won't hear this) until the outputs fail. Yes they can tell if you've attempted to operate otherwise & will absolutely not warranty this folly. Transparent is another networked design that *should* operate with full stability on Spectral but I wouldn't guarantee anything. Unless you have a quality oscilloscope bridged across a Spectral amp's outputs, or a lot of expendable $ & time, then DON'T.