This doesn't really answer your question about Speakons, but the most fool proof way to bridge an amp (for me, anyway) is to take off one of the Speakons and use a banana plug on one end.
For normal use, plug the red and black poles of the banana into red and black on your amp. This gives you 1+, 1_ on the amp to 1+, 1- on the cab.
For bridge operation, plug the banana into both Red connectors on your amp. This gives you 1+, 2+ on the amp to 1+, 1- on the cab.
This way the same cable can be used for stereo or bridge operation and you never get confused on which end goes to the amp.
If you have a double ended Speakon cable that is long enough, cut it in half, add two banana plugs and you now have two speaker cables.
You'll still have to set a switch on the amp to put it in bridge mode, or maybe through the lcd screen, depending how that amp is made.