I want to use the Audiophile 2496 as they can be bought for £15 - £25 here BUT I noticed there are 2 different Rev's, so my 1st question is will either version work out of the box in the 867?
Never had any issues with any revisions of the 2496 under OS 9... but it would be wise to go with the older rev just in case they "cheap-ed out" on some component
Would it be better to use OS9 or OSX (Have access to all up to Panther) for stability due to the DP's?
Dual Processor is stable in OS 9, just runs a little hotter, there is a complete DAW here for OS 9:http://macos9lives.com/smforum/index.php/topic,2716.0.html
Or you can do Panther.
As the Mac will probably/mainly only need to have a Mic/Guitar/Midi KB used with it would it be a worthwhile investment to get mixer (then > 2496) or direct into the 2496?
Well, you will definitely need a small mixer... or if you can find the Holy Grail
for small solo/project studios...HOLY GRAIL MindPrint Trio SPDIF
You can connect via S/PDIF into your G4 mac (if you have a an Optical In Soundcard) with No drivers at all needed for the Mindprint. Or if you are using an Intel MacPro, iMac, or Macbook Pro, directly into the Apple stock digital I/O. Note: Newer iMacs Audio inputs double as an Optical in (Just need a $3 adapter). Your tracks will sound unreal for such a small interface (considering it is a Mixer, an interface with Talkback and 2 headphones outs). Also you can connect 3 different Speaker sets (Monitors) by hitting the buttons on the mindprint (3 Speaker outs). Another route would be connecting the TRIO with the analog IN/outs simultaneously to a 2496 in a G4. The quality of the Mic Pre, Guitar In (with built in compressor), and Line In are equivalent to Top end Pro gear.
Midprint Trio... Ultimate small DAW Miracle: http://www.soundonsound.com/sos/may05/articles/mindprinttrio.htm