Looks like for Ex-Link direct set is `\x08\x22\x01\x00\x00\xYY\xZZ` where YY is 00 to 64 (0% to 100%) and ZZ is the checksum (which you'll have to calculate for each volume level). For MDC it's `\xAA\x12\xWW\x01\xYY\xZZ` where WW is the display ID, YY is the volume (00 to 64 again) and ZZ is the checksum. For these discrete commands it's more common to use some sort of module rather than precomputing all 100 checksums.
