It is possible to use "{CMDSEGMENT:}" with composite (prefix/suffix) commands, however as processing the segment info for those commands is resource intensive, it is disabled by default.
You can enable the "Allow command segment info for composite commands" option on the "System / Advanced" tab of the VoiceAttack options window, however I would recommend finding another way to achieve what you're trying to do.
If you don't have repeated words or phrase segments, you can use the "Contains" operator within your condition(s), in combination with the "{PREFIX}" and/or "{SUFFIX}" tokens.
For numbers you can use the "{TXTNUM:}" token to filter out anything but digits (though this will only work properly if you don't have more than one number in either prefix or suffix).
My personal preference is to use dynamic command sections instead of composite commands, using conditions to achieve the same result instead, which also allows the use of "{CMDSEGMENT:}".