I've just done some listening tests on my all analogue set-up (568.1)

I did -3dB, 0dB and +3dB for the main L & R. (spl corrected)
I did this several times on the same tracks.
The differences a small to say the least, but overall if I had to put them in order it would be;

1st -3dB
2nd 3dB
3rd 0dB

The -3dB just sounds a little more open and individual sounds are easier to make out.

The differences aren't night and day by any means, very very subtle to the point of not being valid due to expectation bias.

This may not be an issue at all with a 568.1 using the analogue outputs.
But then again Trifield width still works on the 568.1...

Steve.