Hi Vintage Vibes,
Please tell us why you are connecting your S1 Pro to your L1 Compact.
Are you adding the S1 Pro to the L1 Compact to augment the sound of the L1 Compact?
Are you adding the S1 Pro to the L1 Compact to use the S1 Pro as a monitor?
Basically, you can connect the
Either way, use a 1/4" (6 mm) Tip-Ring-Sleeve cable. This will give you a balanced connection.
Does that help?