In my experiments I found that it is hit and miss if the QuickTax will even run under Classic. I have installed it from X via Classic and then launched the app and it will hang.
I found if you boot into pure 9 (if you have a machine that still can) and run the app and then reboot into X it will then run under classic. Then there is the the whole printing thing to contend with.
QuickTax needs a good swift boot in the pants.
Don't they have an office in Edmonton, maybe a few ehMac Community members could go over and have a pant kick'n party.