Template:Balanced TRS from S1 to Model II
The output from the S1 Pro System Line Out is a balanced mono 1/4 inch (6.35 mm) Tip-Ring-Sleeve and the input on the L1 Model II is a balanced mono 1/4 inch (6.35 mm) Tip-Ring-Sleeve so use a cable like this.
1/4" TRS Balanced Patch Cable (audiopile.net)