Ummm...do you have another Z2/3 Amiga to check those boards out?
I don't wan't to be a scaremonger, but I used to own an A4000 but I got rid of it after it destroyed a friend's Picasso II and my brand new GVP Spectrum...
My A4000 was pretty faulty and cost me alot of headaches and damages. I moved to an A1200 tower setup and haven't looked back.
I hope your A4000 trouble isn't the same as mine was...