I am glad to hear you got your 4400 working. Another good thing to try is cleaning all the contacts on the logic board - after so many years those pins get dirty. Electronic contact cleaner can be found in auto parts stores here in the US. 

Those adapters are really hit and miss, I own two different 6 switch types just due to some graphics cards not liking one over the other. 

Consider downgrading to Mac OS 7.6.1 from Mac OS 9 - it will be a lot faster. Mac OS 8 would be a good middle point too if you like the platinum grey look over the old Finder.