the cards will work fine in any OS9 compatible Mac with PCI slots, the latetest model beeing the first production half of the so called Dual G4 'Mirror Door'.
Later machines of this type will refuse to boot from OS9.
Best system for Scope under Mac OS is the Quicksilver G4 anything between 500 and 800 MHZ will do.
But: Creamware has never been really good in the Mac domain... and to be honest... OS9 wasn't Apple's greatest hit, too
in fact they already had waved goodbye to 'classical' Mac virtues with the very first release of that OS.
Intended as a patchwork to ease transition to their forthcoming unix-ish thingy named OSX it was never meant to be something on it's own.
That it worked quite well (for some people even amazingly well) is simply due to the fact that the original Mac OS (below the OS9 layer, so to say...) was a very solid piece of work.
If you want to stay in the
currentMac domain with sequencing/recording, the best setup is 'any old box' for the Pulsar/Luna and your sequencer machine connected by 16 channels of Adat IO, preferably by an RME card.
Hubird's system is built like that and a few others here have similiar setups, even in the Windows domain.
Admittedly, the extra RME isn't a cheapo, but it has additional niceties in the digital clock domain (it can improve your signal chain significantly).
Of course any other Adat card will work, too.
Otherwise stick with a Quicksilver Sawtooth model under Mac OS9.
cheers, Tom