Hello Mark,
Let me ask you a question. I installed qemu-system-sparc64 with Solari 9 and 8, and I had the same errors at booting time as reported in this thread.
I used the 20190815.exe for windows 64 bits, with windows 10 OS. QEMU emulator version 4.1.0 (v4.1.0-11789-g013a2ecf4f-dirty)
I also used a VirtualBox VM with Debian 9 to test it and and I had the same error at booting time.
I am just a user, so I would like if you have some updated binary of qemu-system-sparc64.exe for windows to test it.
Thanks in advance. Leo