→What size wire should I use?
Size matters when it comes to low impedance speaker wiring. As the distance increases, consider the insertion loss for a given wire size and then increase the wire size (smaller AWG numbers) accordingly. Pro audio system designers generally look for a loss less than 0.2 dB but that may not be realistic for your situation.
This table is provided to help you understand what kinds of losses occur with different size wire. A 3 deciBel loss is one fourth of your amplifier power, that is, for 100 Watts output, only 75 Watts will get to the speaker.