Did you find this site from the S record header?
One of the two versions probably came from me. I got the KCACR basic off of a real cassette tape. I've tested/verified two versions and released them out on the web.
I know this sounds stupid since you're obviously smart enough do the FPGA work... but have you been jumping to 0000? Are you sure your memory image is good? I can e-mail you mine.
Can you run the 6800 ACIA monitor? I can send you the binary file for that if you want.
Grant