Most NEUTRAL class A mono's

I would have reservations about a $20K active low pass (LPX) myself, but that alone doesn't limit you to the Tidal Impact amps. Pass, Krell, FM Acoustics all make top quality active crossovers that could be substituted as well and accommodate different brands of amps, which really opens up the options. Maybe SS for bass and tubes above? BTW, adding an active high pass to the already existing passive high pass can work well if the former is set to a slightly higher frequency. I've done it on my Genesis along with the factory active low pass.