According to this page (http://"http://archive.digidesign.com/download/plugs/hdmac.cfm") that lists a bunch of OS9 TDM plugins, there was a version of the Indigo made for OS9.
(http://www.vintagesynth.com/misc/indigotdm.jpg)
I have the older Virus TDM running in OS9 (and you can too (http://"http://macos9lives.com/smforum/index.php?topic=1040.0")), but it doesn't read the Indigo patches. So my question is: is there a version of the Indigo for OS9 running around in the wild?
(http://www.vintagesynth.com/misc/virustdm.gif)
Vintage Synth has a nice comparison chart (http://"http://www.vintagesynth.com/misc/access_virus_chart.pdf") of the various versions of the Virus (including the hardware machines).