I thought I'd briefly tell my experience. I bought a G4 Mac Mini from Headgap, an online store that sells reconditioned Macs. I've had Macs since 1984 and certainly had OS9 macs in the past but I was looking for the newest one I could find to make it easier to maintain since I'm not an EE. They warned me that making it boot 9.2 would make the audio problematic. For me, it had no audio when I booted it up (as expected). Also though the headphone jack didn't give me sound. I tried some old Harmon Kardon soundsticks for an old iMac I used to have and that seemed to be recognized, at first. When I moved the machine though, it no longer seemed to recognize them in the control panel. However, the audio did play through them at about a volume of 30%.
I can't change the volume though, and the soundsticks don't have a volume control. It's annoying, but it's more or less what I expected. I mostly got it to run Realmz and perhaps other old Mac software I had (Myst, the Voyager Record, Last Chance to See, etc.). I don't know if anything but Realmz runs yet.
I'll also say that initially, I tried to connect it to a 720P Insignia TV that had a variety of inputs including VGA. That had worked with a HP Mini 2140 netbook I put Linux on but the resolution was quite coarse (looked good though). On the Mini though it gave me the initial splash screen and than it only would say VGA mode not supported. I was using a VGA/DVI adapter to make that connection. So I bought an Apple 20" Cinema Display on eBay which came with the adapter and cables (not all do surprisingly). It has a native DVI connection and was made about the time of the mini so I was hopeful it would work, and it did. The only downside is that the resolution is quite high, 1680 on the high side, which makes OS9 have moderately tiny UI components (but Ok, at least they're razor sharp). Plus the monitor functions as a USB and Firewire hub which is useful. I have to lower the resolution in order to play Realmz or else it's a tiny rectangle on the monitor! ;-)
Anyway, sure I'd like to get the sound to work better, but judging from what I'm hearing here, I'm pretty lucky overall. Maybe some of this will help some of you and maybe we can even get that audio working eventually.