Vertical bi amping Mcintosh MC275 and Rotel RB-1582 MkII

It is done, sound wounderfully wide opened with warmth of tube and tightness of bass.  In this setup doesn't require any external what-so-ever.

28 dB of gain on the low frequency or mid-high amp?Is there a simple dial to control gain?

Both @mijostyn and @georgehifi has given good advice. You shouldn’t try bi-amping the two amps on hand without a gain control switch. In your situation where two amps are not identical, an external crossover is a ideal solution for bi-amping to work and sound properly.

Having said that, two things working against you in what you are trying to accomplish,

1. You cannot by-pass internal crossover unless you’re willing to open up the bottom plate and disengage the crossover,
2. B&W loves power, I am afraid the Rotel amp will not be adequate to drive the bass woofers. More than likely, the bass will be flat and dull. 

I’ve been there, done that (used to own 803S, 804D, 800D2). Without tempering the internal crossover, your best bet would be to try the following amp or something similar with your MC275.
https://www.classdaudio.com/sds-440c-class-d-audio-amplifier.html

Good luck!

There is a standard, I believe it is 28 dB of gain, which amps often stick to. 

Try it, and see if the balance changes a great deal.

However, I feel both amplifiers have enough sound character differences between one another, that you may find a discontinuity in sq between the woofers and the mid / tweeter sections when listening.

Yes, it just "may" take the "coloration bloom" out of the lower mids, and give a more "accurate" representation, depending on where the xover point is between bass and mid driver.
And it’s not like a step off a cliff crossing over from one to the other amp, as the speaker 2nd or 3rd order xover will see that it’s a gradual changeover between the two amps.
Just make sure you try one amp phase reversed as the tube or the solid state may invert phase.

You may like or dislike it digitalgon, depends on your taste in presentation of the source.

Cheers George

What you are describing to do is horizontal biamping ( passively ), and George, is correct. However, I feel both amplifiers have enough sound character differences between one another, that you may find a discontinuity in sq between the woofers and the mid / tweeter sections when listening. Only trying it yourself will determine what you think.

digitalgon 

  Vertical bi amping Mcintosh MC275 and Rotel RB-1582 MkII

Hi all,
I’ve been researching the title project but not getting any productive results. Basically I’d like to know if the volume matches between these 2 amps.

For them to be identical gains, would be very very lucky.

All you have to do is put a $49 Schiit Sys passive at the input of the louder of the two amps an set it just once it so your amps are then balanced to your ear, this also gives the ability to give or take a little mid/highs or bass to balance out bad recordings that are too bright or too bassy.

https://www.schiit.com/products/sys

Cheers George

digitalgon, you can not do this without a gain control on at least one of the amps. It is a bad idea anyway. Get a dbx DriveRack and do it right bypassing the woofer, midrange crossover in the speakers then just dial in the same cross over and slope into the drive rack.