It is pretty easy to test this out for yourself (and preferably blind test it if you have a friend)!
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The idea is to use it in reverse, so take a source like a CD player and plug it into the "output" (that you are actually using as the input) and then select two (of the 4) sets of input terminals to connect to your Hegel and your Adcom setups (which, of course, are in the same room with speakers adjacent to each other). Set both units to "pure direct" (or whatever is closest). Switch back and forth until you have matched the levels. Now you have instant, level matched switching, so you can really home in on any differences you might hear.
I like to use my CD player for this because it has an "A to B" feature on the remote that allows me to continuously repeat playback of a specific short phrase (where I had designated A and B) and I can switch on each repeat to allow me to really home in on the specific differences I hear.
I have still found expectation bias to influence my perception, but it certainly eliminates so many variables!
If you have a friend to help you, establish the correct volume for level matching for each permutation you plan to evaluate. Then you can leave the room and he can swap things around. Ideally he leaves the room (resulting in a double blind) and you come in and do the test. As long as your RCA cords look the same (and you might grab a bath mat to throw over the cords to obscure which runs to which amp), you should not have any way to tell which amp is driving which speaker.
Once I compared two power amps (a respected HiFi amp vs a respected pro-audio amp) using a similar setup with two pairs of identical speakers. I got really excited that I heard a clear (though subtle) difference.
However, then I swapped the positions of the speakers and, sure enough, the shifting of the speaker positions (which I ha set up side-by-side with 1/8" between them) resulted in the differences I heard (ie - my conclusions regarding the amps were exactly opposite). Thus I concluded that any audible differences that may exist between amps was dwarfed by that slight difference in speaker positioning!