Audiolabyrinth, I know of that 2 dimensional soundstage you speak of and it went away when I got my Marantz SA-15S2b. My soundstage is now the same height from extreme left to right (higher, in fact), extends further into my listening room, and has much better layering as you go back. It's not 'Star Trek' holographic but conveys a really nice soundstage, depending on recording.
As for body, that was the first thing that hit me when I first played the Marantz. There was more weight, gravitas and strength in the music, allowing more headroom for that soft pp to loud ff. As it got stronger, realism increased dramatically as playing became more natural. I don't know how else to say it.
As for the resonance tuning, could it be that the Marantz has a more solid build quality that what would tame negative resonance problems? I just tried a quick study with some heavy books on my Marantz and couldn't detect anything amiss no matter where I placed them. Could it be the Vincent isn't as robustly built as the Marantz and therefore benefits from the additional dampening?
All the best,
Nonoise