Horizontal Passive Bi-Amplification
Horizontal bi-amping allows you to use two different types,
models or brands of amplifiers (i.e. tubes on top, transistor
on the bottom). However, we recommend that you use
two identical amplifiers (i.e. same brand and model).
If you must use two different amplifiers, it is essential that
they have the same gain or that one of the two have adjustable
gain so that you can match their gain characteristics.
If the amplifiers of choice do not have the same gain
characteristics, then a sonic imbalance will occur.
For non-matching amplifiers:
since the loads your adcoms present to the Onkyo are 50K ohm and 100K ohm, which should present a load 33.333K ohm load to your pre-amp, which should be easily driven by it, assuming the output impedance of 470 ohms specified in the manual for your record outputs (rec out) on your Onkyo is also put out on your pre-outs. It doesn’t specify for the pre-out, so fingers crossed that it’s about the same as your record outs. the quality of tour interconnect cables and splitters will likely have a great effect on impedance than your mismatched amps.
see this link for how to calculate impudence for dissimilar loads wired in parallel (this is in a perfect world. it’s actually WAY more complicated than that, but this is good enough for what we are up to):
ohms and calculations aside. think of it in these simple terms…
you will be splitting the signal from your Onkyo L and R front pre outputs and sending it to two amps instead of just one. so think of it as now “driving” two amps instead of just one. this puts a far greater load on your pre-amp. most audiophile quality pre-amps are designed with this in mind. but AVR receivers with pre-outs as an add-on or even an after-thought… not so much. don’t get me wrong, i think your Onkyo will drive your amps just fine. but we want to do everything we can to make it easier. this includes:
– high quality splitters
– high quality and as short as possible interconnects (that’s why i like the stubby splitters, why add more cable into the equation if you don’t need to)
to insure against any hum, you will want to place your pre-amp (Onkyo) at least 6” away from your adcoms, preferably on a different shelf. if you can still get away with 3’ interconnects, that would be best.