From what I've been able to find the little Bose speakers are 6-Ohms which is also the minimum rating listed on the Bose amp.  I also found some pictures online of the inside of the Bose speakers and they appear to have a small internal crossover made up of several capacitors so I'm sure it's just a low quality high-pass filter to keep bass from damaging the drivers.

The internal passive crossover seems to make sense because the same model amplifiers are driving 3 different types of Bose speakers (indoor in-wall/in-ceiling, outdoor surface mount and in-ground garden) which all seem to have different sizes of drivers.  Since the amps don't have any settings for crossovers or DSP to match the different speakers, I'm sure all the speakers have their own internal crossover.

Before Ernie corrects me... I guess they aren't really crossovers since the speakers only have full range drivers.  The more correct term would be filter.

Because of this, I'm fairly certain the Sonos Connect Amp will drive the speakers without issues.  I'm sure it won't sound very good, but probably not any worse than it already does.