I called Sonance about this... Their normal in-ceiling speakers (or in-wall) will last for years with no problems. Their speakers are all designed for hot/cold/humid/dry conditions and should see no major issues.
I have installed at least 40 pairs of their speakers in bathrooms and have NEVER seen a pair fail.
I called them in my case because I have in-ceiling speakers on my front porch which is covered. So, no direct rain, but temperature swings from 0 - 100 degrees farenheit plus lots of humidity.
"No problem, should last you for years as long as pure water isn't running right onto the speaker."
Sounds to me like you shouldn't have any problems with any of the major speaker manufacturers products, or even some of the cheaper products.