Re: NHT help
It would be better to connect the 2 SA-2 woofer amps to the sub-woofer output of the Yamaha RX-V2400 with a splitter at the Yamaha RX-V2400 and the two you show at the SA-2s. Then set the crossover in the Yamaha RX-V2400 according to the speaker recommendations. Also it may be that you only need to feed the left channels on the SA2s when satellites are not connected to the SA2s thus eliminating the splitters at the SA2s.
Also you will need to match the SA-2s low and high pass filters to match the crossover frequencies. It may take a bit of trial and error to get this right and it may be best to set the subwoofer a 150 hz and the satellites at 110. That would let the Yamaha RX-V2400's setting have the crossover control.