I'm asking because I wonder if these 100 watt class D monos have enough testicular fortitude to drive <89 dB efficient speakers with grunt and authority. I would completely understand if you chose not to answer the above question ;)
Generally speaking I'm not a fan of low efficiency and hard to drive speakers. This is simply because the harder you make any amplifier work for a living, the higher the distortion, and with that distortion comes a less relaxed presentation (due to the generation of higher ordered harmonics) and less detail (since distortion obscures detail).
89dB is borderline low efficiency. A lot depends on the room and your listening habits as to whether 100 Watts is enough power or not. The speakers in my bedroom system are about 90dB and I play them with an amp that only make 5 Watts with power to spare, no worries. You have to take the room into account.