you need to look at the following sheet in the zip file
rs232c_amp_100223.xls

goto tab ZoneInputSel

0x00:main,
0x01:2nd,
0x02:3rd,
0x03～ reserved

choose what zone you need, and send command,
au_func
２１：HDMI1
２２：HDMI2
２３：HDMI3
２４：HDMI4
２５：HDMI5
２６：HDMI6

goto tab

choose what zone you need, and send command

there was a program ES-Presso that allowed control via rs232 check out
[Link: vibert.us]