^ An AVR's 100wpc rating won't ever match the strength of a dedicated stereo amp's 100wpc. You would notice it specially in hard-to-drive speakers. Just an example, using my PSB T6, my 50wpc NAD integrated amp outperforms my 100wpc Onkyo AVR in music in almost all aspects. NAD sounded more powerful, balanced and musical, while the Onkyo amp sounded artificial.
Using an AVR's preamp section isn't really the way to go. The preamp is really important because in my experience, it influences majority of the sonic character of your equipment. Doing direct mode does not help much, because it leaves you again with that measly current coming from the AVR and it forces your player to be the preamp.
In response to #2, if the genre you listen to are contemporary music like RnB , One Direction or Justin Beiber, playing off music through the AVR should suffice. For critical listening, the image should always be infront because the singer should always be there not going around the room unless the image being projected was a cabaret or a gentleman's club in Cubao. Proper toe-in and optimizing the speaker distance takes care of that time alignment "feature" Audyssey gives you. We also play music true to the way how it is recorded, having a DSP, just colors the sound. It has to be played as is, which actually made a lot of amp manufacturers skip tone controls. Still got something to say but I got a mental block from the lack of sleep I got A/B-ing DACs hehe...