MOS=MorphOS!
Ahh... It's all so clear now.
I was wracking my brain trying to figure out what CBM's legendary semicondictor company (R.I.P.) was doing to cause such a stir! Especialy since the MK4 web site says it supports the MOS 6581! :-)
I keep forgetting that there's a core of users who are retro-enthusiasts, and a core of users who are alternative-OS enthusiasts! Some products, like the MK4, actually straddle both user bases!