It is, i gave a small garden party last summer (about 25ppl) on a 98dB sensitive system powered by 2x15w (2x Pass ACA's in bridged mono config) and it was loud, loud enough to annoy the neighbours, get dancing going on and it was still good sounding. I put them against the wall of my house.
In my house, where i use the same config i measured about 50mW ageraged from 15min listening to heavy dub (bass heavy music) for my "active listening" level (probally arround 80-85dB).
I would love to try such thing with a much more cleaner low distortion amp also, but it's like that low power class D amps always suck and have a (relative) lot of disharminc distortion. Even my SMSL SA36 still sucks a bit on that (altough it's one of the better ones). The good ones are all high powered, to high to use with such a sensitive driver and drive it with a normal input (so the noise level of the system before is not to high). I would like to have the quality of an Ncore or Purifi amp but at 10-20W output, not 400W.