I don't see where the article says that they are. It says that the tubes are designed for musical instrument applications to generate rich harmonics. Essentiall

I don't see where the article says that they are. It says that the tubes are designed for musical instrument applications to generate rich harmonics. Essentially, the distortion characteristics of a tube amplifier are different from those of modern designs, and these characteristics are sometimes desired in for example guitar distortion pedals. Korg has previously released synthesizers and a sampler using vacuum tubes for effect rather than to make them "better" in any objective sense.