I recently got a ZZ9000 and have an issue together with a ReA4091 Z3 SCSI-Controller. My A4000 only boots in this configuration if the ReA4091 is the first card in the daughterboard. If the ZZ9000 is the first card, the Amiga will only display a yellow screen. This topic was already discussed on the IRC recently: https://mntre.com/amiga-irc-logs/2022-11-13.log.html
The issue is gone if any other card is installed between ZZ9000 and the ReA4091 (install order: ZZ9000 - CPLDICY(in my case) - ReA4091).
Another issue seems to be the Z3-Ram of the ZZ9000. It causes Guru’s, Reboots and other “funny” stuff in combination with the ReA4091. When the Z3-Ram is disabled with the “nofast”-firmware, everything’s good.