You are correct-the off gassing thing is a whole other complication to this issue! We did have an experience using a Totem Acoustics flush ceiling speaker in a sauna ceiling that worked for several years, but eventually warped/melted. Right now we are tasked with sourcing a more rugged replacement. When you search for sauna speakers you do get results of quite a few surface/flush models designed to "take the heat" All of them I found also looked like they were not very hifi that I found. We kept digging and came upon the Revel XC Series of speakers-the Extreme Climate models. They are outdoor rated and designed to take the heat of outdoor Summer install in desert homes. Our Revel rep told me that XC speakers would withstand Sauna install. Not sure if this link will post? [Link: revelspeakers.com] good Luck!