Alexxander, You need to sort the items numerically - at present you are sorting them as alphabetic strings. Here is how you might go about it:
#include <Array.au3>
; Simulate reading files
$sList = "8-1.mp3:8-2.mp3:10-2.mp3:8-4.mp3:8-5.mp3:10-1.mp3:8-3.mp3"
$aList = StringSplit($sList, ":")
_ArrayDisplay($aList, "Unsorted", Default, 8)
; Now create a 2D array...
_ArrayColInsert($aList, 1)
_ArrayDisplay($aList, "2D", Default, 8)
; ...and set the [1] element to the number
For $i = 1 To $aList[0][0]
$aList[$i][1] = Number(StringRegExpReplace($aList[$i][0], "[^0-9]", ""))
Next
_ArrayDisplay($aList, "Number column", Default, 8)
; Now sort the items numerically
_ArraySort($aList, 0, 1, 0, 1)
_ArrayDisplay($aList, "Numerical Sort", Default, 8)
; And finally remove the number column
_ArrayColDelete($aList, 1)
_ArrayDisplay($aList, "Final", Default, 8)
All clear? M23