Monoblock Aegirs

Vidar is not a Lin topology. When used as a monoblock, it is simply amplifying a differential signal. It is not bridged."

This only applies to the input stage, output stage’s negative speaker terminal is still at ground potential therefore will only degrade in many parameters when the amp is "bridged", but gain more wattage.
Only amps that are are "fully balanced amps from input to output stage" with no earth ref will apply, like many Class-D’s. .
And here’s what Schiit told Stereophile As I said the output is "bridged"

" In mono output mode, Schiit says that the Aegir will deliver 80W into 8 ohms (19dBW). With a balanced, "bridged output"

As for the OP he will only be using one Vidar in stereo mode anyway only for the bass of both speakers, in the way I suggested he do it.

395garrison OP

A simple way for the OP to find out, is to ask Schiit if a mono’d "bridged" Vidar will be more or less stable into low impedances than a stereo Vidar, also a tell tale is which one has the "lowest output impedance" and "highest damping factor". This will settle it once and for all.

Cheers George

George,
I dusted off the old owners manual because I thought I recalled some bi-amp instructions. Mr. Vandersteen says no go on the horizontal bi-amping with two different amps idea, he gives a lengthy explanation as to why not on pg. 4. 🤷🏻‍♂️ He recommends vertical bi-amping with two of the same amps.

Aegirs probably wouldn’t have enough in the tank for that configuration.

http://www.vandersteen.com/media/files/Manuals/2ce_signature_ii_manual.pdf

Your better to use the Aegir on the mids and highs and the Vidar on the bass and if they are different gains use a Schiit Sys on the louder of the amps to reduce it to the others level then use your Schiit Freya + preamp as the master still.

That’s a really bad idea. Particularly for a Vandersteen which has been phase aligned with such care in it’s design.

You should vertically bi-amp with 2 identical amps. If you doubt me just give Vandersteen a call. They're happy to talk to customers about such issues.

Looks like 395garrison posted while I was writing and even provided the reference from Vandersteen ;~)

That’s a really bad idea. Particularly for a Vandersteen which has been phase aligned with such care in it’s design.

Impossible, if gains of both the amps are adjusted with the Sys to be the same, Vadersteen’s phase alignment will be unaffected as the original Vandersteen xover is still used.
  
Yes different story if an external active xover is used.
  
BTW: He wouldn’t have done bi-amp or bi-wire terminals, and his level controls will screw up any phase alignment anyway once taken off the 0db position.
https://www.stereophile.com/images/archivesart/107vandy2.jpg

Cheers George