Ishom,
The NX4-6000 is an updated version of the NU4-6000.
I have powered a pair of Keystones with a single NU4-6000, channel pairs bridged mono to each 4 ohm sub.
That said, with a three way system, normally I used one channel pair of the NU4-6000 bridged into the sub, and the other two channels for mid/high, the two amplifiers on either side of the stage to reduce cable length.
If one amplifier failed, the system could still be run mono, with one sub per channel, ~3dB less power than in bridged mono mode.
Art
The NX4-6000 is an updated version of the NU4-6000.
I have powered a pair of Keystones with a single NU4-6000, channel pairs bridged mono to each 4 ohm sub.
That said, with a three way system, normally I used one channel pair of the NU4-6000 bridged into the sub, and the other two channels for mid/high, the two amplifiers on either side of the stage to reduce cable length.
If one amplifier failed, the system could still be run mono, with one sub per channel, ~3dB less power than in bridged mono mode.
Art