Soundstage has dimensions of width, depth and height. If you have your v4 set up properly in relation to your MLP and your room is "right", the width should extend beyond the speaker width. The depth starts from the front of your speakers all the way to your front wall or beyond even. With well-recorded material, that depth is composed of layers or parallel planes from front-to-back. Height is measured from the floor to the ceiling and with well-recorded material, you can hear voices/instruments at various heights. I had none of this with my M80 v2.

In Sade's The Sweetest Taboo, the rain is 5 feet behind the front of my M5s. It's a sheet of water covering my front wall. Maybe with a better room and better speakers (?) that depth would extend beyond my front wall. In Belkis, Queen of Sheba: War Dance, the drums at the beginning are at the far left, beyond the width of my M5, wayyyyy back there in the depth of the soundstage and a quarter of the way up to my ceiling. Anything by Trilok Gurtu is layers upon layers for front-to-back soundstage. It's like you can reach out and touch each layer.

Then there's imaging. Instruments in most well-recorded tracks with the v4 are very well-defined and there is lots of space/silence between them. With the v2, the images were fuzzy and piled on top of each other. St. Louis Blues by Wycliffe Gordon is absolutely spectacular and seductive and is a good example of what very good speakers placed well in a good room with good EQ can do.

The above is all 2.1.

There is no difference in audio quality between the 6500 and the 8500. You should definitely be able to hear a difference between the 6500 and your Sony if you calibrate your room using Denon's Audyssey. If a receiver doesn't have XT 32 or equivalent, I stay away from it. I can't say enough about my Onk and its implementation of XT 32.