To bridge an amp, usually 2 channel, but can also be done with a mono (sub amp) you have
+ - and + -
The two channel has 2 channels that allows you to use two speakers, but with bridging the amp you take the + from one side and the - from the other, bridging them.
Now with your sub the MTX 6000, what ohm is it rated? single four, dual 4, etc, etc?? You dont want the amp to go into protection or blow. Also what exact model of alpine do you have? Do you have a link?...