Hi Arno,
This ought to open any file with the default application:
import clr
clr.AddReference('ProtoGeometry')
from Autodesk.DesignScript.Geometry import *
import sys
pyt_path = r'C:\Program Files (x86)\IronPython 2.7\Lib'
sys.path.append(pyt_path)
import System
import os
#Assign your output to the OUT variable.
OUT = os.startfile(r"C:\Taco\music\De Kift - Bal\01 Bal.mp3")