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Here's how to connect two L1® Compacts. Click the picture below to see more details.
In the video you mentioned, the fellow is making the connection from the first L1® Compact line out to the second L1® Compact channel 1. This is not recommended because this will run the signal on the second L1® Compact through the ToneMatch microphone preset. You want to connect to the second L1® Compact through channel 2 with the ToneMatch switch set to Line Level.
The most reliable connection is to use a balanced cable. If this is a fixed installation, that's a one-time inconvenience.
If you want to use a wireless connection you will replace the orange line above with a transmitter and receiver. You can use Bluetooth or other wireless device.
I often use a wireless guitar transmitter and receiver with great results.
How far apart will the two L1® Compacts be? Are there walls or other obstructions between the two locations? Is there a microwave oven in the vicinity? That can interrupt a Bluetooth connection.