Here is the issue with using 16 gauge to hook up the M2-ATX and I was tricked by it when I did my first installation, too. The longer the wire, the more resistance. Resistance makes wires heat up and if you don't use the proper gauge wire, you could end up with a fire hazard, worst case.
The M2 has smaller gauge wires going into because they are SHORT. This leads people to believe that they can extend them with the same gauge wire. Untrue, for the reason above.
To figure the proper gauge wire, you should use a power calculator and the anticipated load on the wire. That will tell you the right gauge to use. If you don't feel like doing that, then at least look at the table in the FAQ that advises on the right gauge to use.
You will need to know how many amps your system will draw, but since you are using the M2-ATX, it is a 160 watt device. For safety, assume 200 watts. Using Watts = volts X amps, you can solve 200 = 12 X amps or 16.6 or 17 amps. According to that table, you can run up to 30 feet with 8 gauge wire but only 4 feet with 16 gauge wire.