Tripper,
I also have NAD power amps in a second system that are bridged mono. I found that by far the best sound IMHO was achieved by isolating right and left channels. No splitter used in this configuration. The L and R fixed level preamp outputs are each connected to the left channel input of a power amp. This is required when operating in bridged mono mode. One power amp is then connected with a pair of matched speaker cables to the left speaker (one run to the +/- bass connections and the other to the +/- treble connections). Same thing for right speaker with the other amp. This gives complete channel separation and provides plenty of clean power.
I also have NAD power amps in a second system that are bridged mono. I found that by far the best sound IMHO was achieved by isolating right and left channels. No splitter used in this configuration. The L and R fixed level preamp outputs are each connected to the left channel input of a power amp. This is required when operating in bridged mono mode. One power amp is then connected with a pair of matched speaker cables to the left speaker (one run to the +/- bass connections and the other to the +/- treble connections). Same thing for right speaker with the other amp. This gives complete channel separation and provides plenty of clean power.