First of all, the speaker wire is almost irrelevant, that has been debunked many times although companies like monster cable insist otherwise. They are just a marketing company with pretty packaging and monster mark ups for it. Your statement of 14 gauge is enough.
Secondly, as Doug Blackburn constantly points out; you cannot blow speakers, as most people view it. A common myth. While, in this case, there is the possibility of some shorting going on there are only two reasons speakers blow; clipping & distortion.
I remember reading a serious Eopinions piece where someone claimed you must never use 50W speakers with a 100W amp very funny. Tell that to most large commercial or theme park installations world wide.
Most amplifiers, produced by any manufacturer, today are over run on specs particularly output. It is well known that in independent tests we read about around the web, most amplifiers are at full output, ie. not producing any distortion or clipping, at half their volume tuning level.
Above that anything goes, it gets hairy with distortion or clipping produced being subject to everything from the efficiency of the power system (which might be true in your case) to the type of sound being played to the input device, cd/mp3 etc., that is translating the signal noise. The greatest amp in the world can suffer crap input devices or a poor power source.
You blew not one but two sets of outdoor speakers, its unlikely its the speakers. You need to talk to not only someone who knows speakers inside and out but also know amplification systems and related hardware.
I bought my outdoor speakers from a real speaker manufacturer (see above post) TIC Corp, www.ticcorp.com
and in discussing accessories they recommended their partners Parts Express www.partsexpress.com
who do everything to do with speakers and related technology. You can even ask to speak to their well known speaker designer Darren Kuzma. This guy has a great reputation. He might actually enjoy your unusual problem as an intellectual exercise.
Without actually seeing your installation and its specifics which is always hard, the advice can only be general but 99% of the time that's all it takes. See their website or give em a call, its an 800 number and you got nothing to lose.