Now for the fun part: cutting some wires...

Make sure to cut the proper speaker cables! Check twice, cut once.

Locate the Left/Front and the Right/Front speaker cables coming out of the radio. There should be two wires for each speaker cable, a Positive and a Negative.

Use a pair of wire cutters to snip-snip those two cables. Don't cut too close to the radio -- make sure that you leave enough length to strip the wire and reconnect it in the following steps.