We never resolved it, got a new 4000 board and it ended up having issues as well. Now about to try on yet another board. I think its safe to say these new 4000Di boards are not as good as other versions.
I have the 4000T version in my machine and have ZERO issues with it.
I have a desktop A4k mobo with Buster 11 in a Micronik BigBox Tower. Initially had the CybervisionPPC graphics card with the Cybergraphx software, later I changed to a Voodoo4 in the Mediator with Picasso96.
I have a weak remembrance that I initially had problems with the Picasso96 software as well, because there still were some parts of the Cybergraphx soft left on the disk and IIRC, Cybergraphx has to be removed completely in order for Picasso to work correctly. But this is just from my memory - and it is rouhly 15 years ago, when I switched to the Voodoo...