9.2 was designed only for those with G3 on board processors after the Powerbook G3 Kanga (the 250 Mhz Mac) based on the same form factor as the Powerbook 3400. Sonnet might have an update to allow 9.2 to work, but you'd have to check with them. 9.2 also is there to optimize performance with the Classic environment of Mac OS X, which the Kanga of course can't access either.
I agree that you can update 8.5 to 8.6 with the update that Jan suggested. Conflict Catcher sadly is made by a company that no longer exists, so getting an update to ensure it runs with 8.6 or later is no guarantee. However, I've found many issues with the Extensions Manager can be isolated with the base extension set, and then building on it. I've run every Mac system since 6.0.5 on a Mac II, and even played some with the original Macintosh system.
PCMCIA USB card, although I'm uncertain if it worked with Mac OS 8.5. I only started playing with it on 9.1.
It was a slow USB 1.1, but at least it worked for any wall powered USB device. Not sure if it would be compatible with the 1400 either. You could consult with them what they may have in old drivers.
I agree that 8.6 was faster overall than 9.1 needing less overhead, but a sufficient size hard drive should help. Macs have always worked best when you allowed the hard drive at least 15% free capacity in addition to system specifications.
Lastly, you'll find this user tip for finding old Apple software useful:
How to find Mac OS 9 downloads?
and many http://www.apple.com/usergroups/ have users of older Macs, and http://www.lowendmac.com/ an excellent source of old Mac information.
