Eight months later, ya never know when your old thread pops back up to the surface !!
I never heard of the PAC version of the ST-140 Bob, you might want to call B&K and talk to Jerry the tech man, nice guy, he'd probably be able to tell you more about it.
On a side note: My M-200's sound totally awsome !
They have a big tube sound and easefullness not associated with many solid state amps in addition to a huge soundstage and vice-grip bass.
I'm glad I sent them to John at Musical Concepts, his mods are everything they say and then some.