For some reason Firmware rev. 1.7.5 has had problems with consistent volume levels. I went back to 1.7.2 (hint: always save downloaded firmware revs) and the problem has faded some, but not entirely. Time to do a full factory reset with 1.7.2 loaded.
On several sites, notably AdvRider, there've been reports of near catastrophic failures. I can only assume these are real problems, but I've seen none of them with my 20S. I even offered to test one of these problem-prone units; the owner, understandably, declined.
Overall, writing Sena customer support (go for Martha, Agent #5!) is productive. After that, Sena Inc. doesn't say anything useful. I don't count announcing new releases (bicycle helmet, H-D beanie) as useful. It's the later that keeps me from being wildly enthusiastic about Sena. OTOH, TomTom proved to be almost equally "tits on a boar hog" when I asked about the video camera (one sale lost). [/ big shrug]
Videos about 20S installations with Alyssa (sp??) are useful. For example, she has some good tricks about mic mounting for open helmets.