What’s the Right Power Amp Ratio For Bi-Amping?

I think I should have said:
A 100 W/ch amp produces 26 Vrms = 40 Vpeak = 80 Vpeak to peak . So the internal DC voltage rails would be that plus a little more, +- 43-46 Volts.

Anyway, the story still holds. Whatever those rails are are the absolute limits of your output. Since gain is fixed, your maximum input is limited before you clip.

Best,
E

Thanks Erik. The thing that I’m looking to leverage is the impedance curve with a modest amp powering the high frequencies. I have a NAD 2700 for the low frequencies, with 150 watts per channel into 8 ohms, it’s quite capable. The other amp I have is a NAD 3225PE with 40 watts per channel, an integrated amp with external pre-amp in/out jumpers so i can use just the power amp section. The previous setup had that amp acting as the system preamp and low range bi-amp powering the same speakers, and a 3220i for the highs - that combo worked very nicely. The game changer was finding the 2700 amp for a bargain. 

It doesn’t sound like you are getting advice from anyone who has tried bi- amping. I have. First-You just need to try it and see if it sounds good to you. No rules will help guide you in my opinion.  I use two Bedini class A amps to bi-amp. The 25 watt is used for mids and tweeters. The 100 watt is used for woofers. These are excellent sounding amps individually. Bi-amped gives an amazing  improvement. I’ve used them successfully with passive and active crossovers. Fire up the amps you were thinking of using. You can’t hurt anything if you don’t drive the speakers into distortion. 

I believe the "gain" needs to be the same.

Check out ask Paul on utube. (from ps audio)