You have good speakers. They should be capable of good imaging as long as the speakers are positioned so that the tweeters are level with ear height, within +/- 10 deg. or so.
I have them symmetrically positioned relative to the listening position and only DSP tune the summed response below my room's transition frequency, since the speakers are already flat on-axis.
I would measure their frequency response at the listening position with REW. Even though the speakers are flat on-axis, room reflections may adversely affect the frequency response at the listening position. For me, this was more of an issue in my family room, where the speakers are over 3m from my listening position and the room is asymmetric. In my office my speakers are less than 2m from my listening position, and DSP optimization doesn't have much impact on imaging.
They cannot sound the same in terms of timbre or space, not even considering the interaural crosstalk dip at 2 kHz.
I agree they will not sound the same, and that there will be a difference in terms of timbre and space, but does that difference mean that you cannot obtain good sound staging with solid images using two speakers? My experience with my systems tells me no. Both of my systems sound stage very well and produce solid images using two speakers. The posts in this thread by
@tmtomh and
@Hear Here provide similar experiences.
Anecdotally, a few months back, after tuning my family room system, I had some friends/family members sit in my listening chair, close their eyes, and listen. They were blown away that the music was being produced by only two speakers (and a subwoofer). More than one person noted that it sounded like the singer was actually standing in the middle of the room.
As stated by Toole, "draw your own conclusions. It may be that 'one size does not fit all.'" The impact of the room on the sound is significant, and every room is different.
I have never played with a center channel, and perhaps it will improve sound staging and imaging even further. I don't know, but I do find the subject intriguing. If the cost of another speaker and electronics to implement that are not an issue for you, perhaps give it a try.
@gnarly seems to like it.