OK, I finally got around to doing a direct comparison of the two speakers for center channel duties. See this thread that got the whole thing started for me.

I have been happily listening to my in/on wall system for the past ~2 years now. After reading the debate and discussions of horizontal vs. vertical center channels I had to try it for myself in my listening environment.

Starting off I recalibrated my system just to make sure everything was properly level matched and set with my standard in/on wall VP150. I then replaced it with the in/on wall M2 and performed calibration again. I had to bump up the center channel level for the M2 by 3 db which makes sense looking at the specs between the speakers. So, for switching back and forth between speakers I always changed the center channel level to match the speaker being used. Although this has nothing to do with real life listening, I already noted that the pink noise from the receiver for level matching had a much closer 'tonal match' to the left and right channels. Also note that I keep the EQ defeated on my receiver which is personal preference. i tried to keep the comparison as uncoloured as possible.

So, on to the real world then. My wife was interested in this so she actually sat with me and helped me with the comparison.

Music:
I listened to DM and TR at Radio City on Blu-ray. I noted that the the VP150 kept Dave's voice very anchored in the center and had a 'raspier' sound compared to the M2. I found the M2 created a more seamless soundstage with the front L&R channels.

Also listened to Alice in Chains "Your Decision' from the Black Gives Way to Blue album. (Thanks to Riker for introducing me to that album!). Both my wife and myself noted a 'fuller' sound and no noticeable off axis changes. I have one chair that's quite far to the right side of the room so my wife and I took turns between that seat and the sweet spot in the center. Again the VP150 sounded thinner and definitely did not fare as well in the bad chair.

Ok, M2 is winning so far, now on to movies.

We used the new Star Trek movie on Blu-Ray to evaluate any changes in dialogue between the two speakers. Started with the intro scene and then also went to the hangar scene where they are boarding the shuttles from Star Fleet Academy to go to their assigned ships.

In both cases we again noted that the dialogue was more intelligible from the M2 in both seating positions, although it was a larger difference again in the bad chair. Two particular things stood out however.

First, the horns that play during the opening Paramount scene as the scene fades into the space action - this had a far more natural and impactful sound with the M2 over the VP150. There's also a part where a woman gets sucked into space through a hull breach - just before she gets sucked out she screams amid the rest of the explosions that are happening. My wife turned to me and said she hadn't noted the scream with the VP but heard it with the M2. I heard it both times but I would agree it was clearer with the M2.

So, to sum it up, the VP150 is not bad by any means, but compared back to back with the M2 in my room with my equipment the M2 is clearly preferred.

I think this is a record long post for me!
_________________________
Dan
On-Wall M5HP LCR, QS8 & EP500 in 7.1