Hi there...
Your threads were part of the prompt to put some of this up... I read through it and although you've improved it somewhat which is great, it's not the recommended way, although you do have limits with the 1907 it seems.
By setting everything to 0 on the S550, you are infact still -10db on the LFE...
What speaker sizes do you have configured on the Sony?
No, the Denon 1907 has the 15db boost on the .1 channel for Ext In, which I set as soon as I got the S550 as I'd already read about bass management. I have my speakers small, so I'm using the full +15db. So I am handling that correctly.
The issue with setting the output levels on the S550 to zero is a different one. I was under the impression (as were a few others) that the Amp would essentially do nothing to the multi-channel signal, except amplification per the main volume and the .1 boost. Therefore channel levelling for the speakers would need to be applied on the Sony.
Except this isn't the case, the amp does apply its own channel levelling to the Exit In (other amps may work differently) so by putting levels on the S550 I effcetively doubled all my room levelling adjustments, which in particular murdered the bass as the sub is at -7db on the amp. When I copied that to the S550 it left my .1 channel 7db lower than it should be.
There are also two other things that can mess up the multi-channel out on the S550, no matter what amp you use. The default ARC setting compresses the signal, plus if you have the primary audio output set to optical (and possibly others as well, I haven't tried), while the 550 still sends the multi-channel signal via the 6/8 way RCA, for some reason it takes out all the bass information as it does so. So if you are listening via multi-channel connector, its essential that the primary audio be set to that on the 550.