Installing OS 8.6 on a 9.x iMac, Downgrading Mac OS Options

[abbie]

I was thinking of buying a used iMac which comes with OS9.x. I then wish to install my music software currently running on an older iMac with OS 8.6. I was thinking of initializing the hard disk and then installing everything fresh on the new machine using 8.6. I want to do this since I know 8.6 works well with what I am currently doing. My concern, however, is whether I might run into trouble with firewire support and other firmware/microcode issues. Does anyone have any ideas? Thanks...