Bi amping with two different pairs of monoblocks

(Knotscott) My suggestion eases the BASS Burden of the high pass amplifier relying on the speakers existing crossover to fill the Original Designers aural goals. Most definitely if going full active crossover, I would go DSP crossover to allow all manners of parameters to adjust

The problem with DSP active crossover is you are stuck with the dac that the manufacturer happens to use.

I use the MiniDSP SHD as an active crossover, feeding two powered subs and a Benchmark AHB2 amp for the ATC SCM7's.  Digital is pass through to a Benchmark DAC3.

Bi-amping isn’t something you do half-baked.  Y cables will attenuate the signal somewhat, but the real point has been made above.  If you are going to biamp, you should be using an active crossover between your preamp and the power amps. That is the correct "Y cable." 

I have tried the method above and it may sound cool at first but you will soon realize the imbalance in power between the monoblock pairs unless they are identical.  Good crossovers have gain adjustment to get it right. 

I would look for a good analog crossover. Marchand makes some decent ones without being too budget-crippling and Phil will answer your questions directly. 

I should also say that bi-amping really only makes sense if you can bypass the crossover in the speakers. 

     As others have pointed out, no 2 amplifiers, especially if from different manufacturers, will produce the level of sound from the same preamplifier input signal,