I don't really understand what DAW users do, and how bound DAW are to the CPU or the Bus/interface.
under MacOS Classic and windows, most devices come with
ASIO drivers. this is what you should look out for when buying an interface.
ASIO is widely supported by audio apps (with protools beeing the only relevant exception.)
this driver, which is installed to each app you want to use it with, allows a more or less
direct access from music apps to the hardware - unlike the normal device driver (a system extension), which communicates with the OS9 soundmanager only.
this means, among other things, that latency is lower and your audio IO settings can be saved individually with the project file.
ASIO is also more flexible and more stable than soundmanager. it allows you to choose whether you want to prioritize latency or CPU hunger of your audio streams (by changing the buffer size)
there is also an ASIO driver for soundmanager itself, so that you can have an incest system where your music app uses your MacOS9 settings. best of all, in my opinion, is that you can run ASIO drivers in parallel, so that you can have you music recording app using ASIO MOTU, while in background your sample editor application uses ASIO soundmanager, and the finder the soundmanager itself.
it could be burned up if hot plugged.
hoptplugging is a bad idea anyway.
even RME and motu interfaces, which come with proper driver software, tend to be not found when you turn the interface on for the second time while OS9 still runs.
so you might have to reboot from time to time when you change connections often.
Is there a better 1394 audio device for OS 9?
in case there is no OS9 support for the mykerinos boards, the PCI solutions of RME - used with an external clock - should be the ones with the "best" sound converters. those start at USD 800 second hand. for the average user a behringer interface with firewire connection - starting at USD 15 - is all you need.
the cheapest 8-channel solutions are probably the ones from m-audio. but their older interfaces are often not copmpatible with later OSX versions and they tend to be picky with which applications they work.