You have 200 audio files. One hundred of those files are named DRUM CLOSE 001, DRUM CLOSE 002, etc. and the other 100 files are named DRUM OH 001, DRUM OH 002, etc. You want to mix DRUM CLOSE 001 with DRUM OH 001, DRUM CLOSE 002 with DRUM OH 002 and so on.

Here is an example script that will accomplish this task:

 

tell application "Myriad"
set theDestination to choose folder

begin processing with name "CLOSE + OH"

repeat with theNumber from 1 to 100
set theNumberText to text -3 through -1 of ("000" & theNumber)

set theCloseFile to first item of (every entity whose name is "DRUM CLOSE " & theNumberText & ".aif")
set theOHFile to first item of (every entity whose name is "DRUM OH " & theNumberText & ".aif")
set theOutputFile to "DRUM CLOSE+OH " & theNumberText

process sources {{|entity|:theCloseFile}, {|entity|:theOHFile}} with instructions {} to folder theDestinationwith filename theOutputFile
end repeat

end processing
end tell