My initial intention when opening this thread in my browser was to actually share my opinion on the depth and spatial resolution. I'll try to convey also what I think Bo is meaning when he refers to 2D and 3D sound. As English is not my first language, I should apologies in advance for the occasional typos (the post is quite long). Also, since the atmosphere here is a bit "hot", and I was made aware a few times that I might come across as overconfident and/or patronizing, I should also say that this post is in no way meant to be condescending. (I write in English mostly technical/scientific stuff and that is why I might sound rigid and/or overconfident). So here it goes:
IMO, speaker placement is the most critical detail for obtaining a good depth and spatial resolution. Changing speakers, amplifiers, cd players, cables, etc. can only do so much if the speakers are not properly placed in ones room.
I'll start by note that most often people make sure that the speakers are orientated symmetrically with respect to their listening position, i.e. have the same distance and the same orientation and toe in. Unfortunately, very often that is not enough for obtaining the 3 dimensional sound often referred by Bo. While one obtains a centered voice and, for example, the guitar on the left side and the bass on the right side, everything is pretty much in the same plane, i.e. we have the 2 dimensional sound as referred by Bo. This happens because very often the walls in one's room are not identical from an acoustic point of view. As a result, even though the two speakers are placed symmetrically with respect to the listening position, their frequency response (and wave characteristics) of the two speakers are not similar at the listening position.
I'll give two common examples. First, below 300 Hz, the two speakers can have significantly different responses even when the two speakers are placed symmetrically with respect to the room's boundaries. (This happens because we have low standing waves formed due to reflections between the walls of the audio room, but also between the walls of other neighboring rooms with respect to which the speakers are not positioned semitonically.) A second example, is the case of L-shaped rooms, where one speaker is placed close to a corner while the other one close to an opening. In this case the speaker in the corner will not only put out more bas but will always sound a bit louder than the other one. Unless special measures are taken, both these situations will lead to a partial (or complete) loos of the three dimensional spatial information recored on the album.
The easiest way to solve this problem is to use a room correction software, which is what Bo is actually doing. He is using as pre-amplfier a high-end Onkyo home theater preamplifier which comes with Audyssey Pro software. Among other things, this software makes sure that the two speakers have identical responses at the listening chair. I have actually told him quite a few times that I believe his claims. However, I have also pointed out quite a few times that the timber of instruments is most often more important that the stereo image sound stage.
I'll stop here as the post has gotten very long. If the discussion goes well and people are interested, I will also post my thoughts about the effect of room correction on the timber.
Paul