No valid btrfs filesystem is being detected on the cache device, assuming you are sure the filesystem was btrfs it was wiped or similar, best to restore from backups.
Then and assuming the emulated disk is mounting correctly you can rebuild on top, keep monitoring the disk, especially this one:
ID# ATTRIBUTE_NAME FLAGS VALUE WORST THRESH FAIL RAW_VALUE
187 Reported_Uncorrect -O--CK 098 098 000 - 2
Parity can't reliably rebuild any disk since there were errors during the sync, disk5 appears to be failing, there's no SMART report for disk9 in the disgs posted, please post one.
There appear to be some issues since v6.9-rc with the LSI driver and 8TB Ironwolfs, possible different capacities also, not sure if it's any different with v6.9 final, but likely not.