Thank you all for your reply and help. I just wanted to post an update on my little project. I gave up using A2090a or A2091. I was lucky to purchase DKB 4091 SCSI II Controller at a reasonable price!
This controller worked out of the box on my A4000D. I configured ZIP and PZ0C in Devs/Dosdrivers and now I'm able to access my ZIP drive and also able to read/write on FAT16 formatted Zip disk. It's very useful to transfer files from my computer with a USB ZIP drive to Amiga.
My A4000D Configuration:
* 68040 at 25 MHz
* 12MB onboard Fast RAM
* 256 MB BigRamPlus Zorro-III
* ELBOX FastATA 4000 MK-VII CF/SATA Zorro III
* IDE Pioneer CD-ROM Drive
* 32MB CF Card as IDE HDD
* Zip 100 External SCSI Drive
* External SCSI NEC CD-ROM Drive
* DKB 4091SCSI II Controller (Zorro-III DMA Fast SCSI-II - only works with a revision 11 Buster)
ELBOX FastATA 4000 MK-VII shows as 2nd.scsi.device
DKB 4091: scsi.device
I used FormatZIP from Aminet to format ZIP disks in FAT16. here is the link: https://aminet.net/package/disk/misc/FormatZIP
Here is the drive speed which seems very slow, Any suggestion to improve the speed of ZIP Drive, or this is the max I can get
I'm going to use my ACARD AEC-7730 with SATA SSD with the DKB 4091 and I will create a new post to explain the process and speed benchmarks.