Bi - Amping

Sounds like a valid experiment. 
I might try this instead for level adj.:
http://https//www.amazon.com/dp/B01CX82KH2/ref=cm_sw_r_apa_i_71mFEb1H6AQJS
Then you can hear from your listening position if it is worth pursuing.
Try it with cheap cables first.
Let us know how it works out.

Ensure that the gain on the different amplifiers are the same.

They won't be, and that's what the $49 Schiit Sys passive is for.

Cheers George

Ensure that the gain on the different amplifiers are the same. 

lordrootman OP

Halo A21+ on the mids and highs, because it’s "high bias Class A/AB operation" John Curl design, which will be better for the mids and highs.
And probably the Anthem ( Sixteen bipolar output devices per channel ) on the bass for the current in can deliver into 2ohms

And the Rotel Michi having 100ohm output impedance will have no trouble driving any combinations of amps you have

To me if you have the amps, it’s well worth doing as it will cost next to nothing to do and you’ll gain from it.

Cheers George.

... what are the consequence or disadvantages of not using the same Amplifiers ?

Assuming you are referring to passive biamping (i.e., without using a crossover device between the preamp and the power amps) the advantages and disadvantages include the following:

Advantages:

1) A modest increase in maximum power capability, perhaps just 2 db or thereabouts depending on the speaker’s internal crossover point and crossover slope and on the power capabilities of the two amps. Not sure how helpful that would be, not only because the difference is small but also because all four of the amps you mentioned (one of which is an integrated) are fairly powerful.

2) Possible improvement in the sonics of each amplifier, since it would only have to provide current and power in part of the frequency range.

Disadvantages:

1) As George indicated you would have to provide a means of matching the gains of the two amps, such as the device he suggested.

2) Increased loading of the preamp, i.e., the preamp will see the combined input impedances of the two amps (in combination also with the impedance of the Sys or other gain matching device), which will be much less than either of the individual impedances of the amps. Depending on the design of the preamp that stands a very good chance of applying even though you would be using RCA outputs to one amp and XLR outputs to the other. Many and probably most such designs supply the same signal to their RCA output connectors that is supplied to one of the two signal pins on the XLR output connector for the corresponding channel. That may or may not be a problem depending on the output impedance of the preamp, on how that output impedance varies over the frequency range, and on the input impedances of the amps and the gain matching device.

3) Possible loss of coherence in the presentation, due to the two amps having differing sonic characters.

4) The need for additional cabling.

5) Increased potential for ground loop issues.

The bottom line IMO: It’s probably not worth doing. It will make a difference, but not necessarily for the better.

Regards,
-- Al

@georgehifi
my preamp is Michi P5
I can run Two amplifier at the same time one on balance XLR and other RCA
I was thinking anthem for LF harman Kardon for HF ?

That’s fine so you won’t need "Y" connectors.But unless you have individual level "set controls" for both outputs and a master on that pre to then raise them both up and down together, your going to need a Sys passive on the louder of the two amps as per my diagram so you can equalize the gains.. https://ibb.co/QpmW5mh

Cheers George

http://www.rotel.com/sites/default/files/product/manuals/p5_om_en.pdf

Preamp Output w
See Figure 3
The P5 RCA-type output connectors are compatible with most power control amplifiers. As always, select high quality audio interconnect cables. Connect the left and right channel outputs of the P5 to the corresponding inputs on the amplifier or other component.

NOTE: There are two sets of RCA outputs on the P5. The second set of outputs may be used in custom system configurations to drive a second power amplifier or to supply a signal to a special signal processor.
Balanced (XLR) Output e
See Figure 4
Two pairs of XLR balanced connectors supply an analog output signal from the P5 to a power amplifier with XLR balanced input connectors.

NOTE: Do not connect both the RCA and XLR to the same control amplifier at the same time.

@erik_squires 
no for two channel listen 
im using Michi P5 preamplifier 

@georgehifi 
my preamp is Michi P5 
I can run Two amplifier at the same time one on balance XLR and other RCA 
I was thinking anthem for LF harman Kardon for HF ?

I'm not sure what you mean in this case.

You want to mix amps in a home theater?  That's fine.

If  you want to mix amps that go to 1 speaker, so long as you have separate inputs and level controls on the amp, easy.

Bi - Amping

I want to Bi-amp my speakers with different amplifiers / and diff brands
A21+ Anthem STR amp harman Kardon Signature 1.5 Citation 7.1
what are the consequence or disadvantages of not using the same Amplifiers ?

lordrootman

No problem you can do it with different amps, you will have to do horizontal bi-amping
And need a pair of rca "Y" connector and a passive volume control on the louder of the two amps so you can match the gain/s once set you will not have to touch it. 

Horizontal Bi-Amping https://ibb.co/QpmW5mh

$49 Passive pre.  https://www.schiit.com/products/sys

RCA Y connector  https://www.musicdirect.com/connector-upgrades/audioquest-hard-y-adapter-rca-splitter-1x-male-to-2x-female

 Cheers George