T4S/T8S Headphone Output to S1 Pro as a Monitor
You can use the T4S/T8S headphone output (using a 1/4 inch (6.3 mm) Tip-Ring-Sleeve TO 1/8 inch (3.5 mm) Tip-Ring-Sleeve adapter cable)) to connect to the S1 Pro Aux Input.
The S1 Pro Aux Input (Channel 3) is 1/8 inch (3.5 mm) Tip-Ring-Sleeve. This is intended for stereo sources like the headphone output of a computer, tablet, phone or T4S/T8S headphone jack output.
Note: This connection is unbalanced, and not recommended for cable runs exceeding 6 meters (20 feet)