Also with a biamp setup, you'll gain some tweeter protection from huge bass transients that -- when clipped -- would otherwise send peak-power level high-frequency transients to the tweet.It should be pointed out that this is only true, to a major degree, if an active crossover is used, ahead of the amplifiers. Which in turn would have significant downsides, particularly in this case as others have pointed out.
In the case of passive biamping, both amplifiers have to swing an output voltage corresponding to the full frequency range of the signal. So in a passively biamped arrangement the likelihood that the high frequency amplifier will be clipped by bass transients will only be reduced (compared to using that amp full range) to the extent that its voltage swing capability increases as a result of the reduction in the amount of current it has to supply, and chances are that increase in voltage swing capability will not be all that great.
I make a point of mentioning this because I have seen many posts here discussing the possibility of passively biamping with a low frequency amplifier having vastly greater power capability than the high frequency amplifier. Which would result in most of the power capability of the low frequency amplifier being unusable, because how much of its power capability could be utilized would be limited by the clipping point of the high frequency amplifier.
Also, as you pointed out, in this particular case the relatively low crossover frequency is an additional reason why a large power disparity between the two amps would not make sense.
Regards,
-- Al