I know you proposed Mega Filter in the past. However, I do not really like that extension and thus bought another one for Ajax filtering which – of course – doesn’t work out of the box.
I was looking for a solution in this forum or elsewhere but couldn’t find any. If you find the time to look into this at some point that would be great. I uploaded the extension here for you to test with it:
I will use the standard OC filter until then which isn’t too bad also. So no worries!