Thanks all for interesting suggestions. Especially to @atmasphere – maybe I hear some Doppler effect, yes. At least, so far, these small speakers sound much better with well-recorded ‘sparse’ music than with high dynamic multi-instrument rock. Like Shelby Lynne: Just a little lovin’ (though I have yet to hear a system where this album sounds bad). However I realize that my initial post may be premature. The FR2 speakers need some weeks to open up, according to reviews.
BTW, these speakers will eventually replace my trusty old Sony SRS-ZX1, that are even smaller than the FR2, and yet go down to 60hz or so. This is due to a C-formed channel at the back that Sony calls a «Mobius duct», leading to the bass port below the single driver. I like this analog domain type of modification, avoiding electronic equalizer glare, but I don’t think Sony ever developed it further. However, even if the Sonys go lower, the FR2s are better from midtone upwards (clearer, more air, space), so I hope they break in, over time.