I have been using the Magnepan Tri-center technique for a few years and I remain very happy with it. I did it with a pair of old SMGs on either side of a 96” projection screen and currently a 65” LED panel, and the MGCC3 mounted in free space over the screen. Main left and right speakers were 1.6/QRs. I‘ve also done it with all JBL 305P MKIIs (see attached photo) and with all Adam Audio T5Vs across the front instead of Magnepans. In every case, each speaker was EQed and level- and delay-coordinated with DSP. The results were great in every case. I settled (most decidedly) on the 3 center speakers being time-aligned with each other and the “center center” doing about 95% of the work, using only the “side centers” to tweak vertical and horizontal phantom center image position. The added subtle sense of spaciousness from the decorrelation effects of low-level comb filtering is a pleasant side effect if you have become accustomed to it from decades of two-channel stereo like me.
If you try any of this without DSP control, you may become very quickly frustrated. With DSP and some patience and time you can dial things in pretty tightly. You get a fairly stable phantom center image wherever you want to place it.
Note that a pseudo tri-center effect can be done by feeding a tiny bit of the center-channel audio into the front main left and right speakers instead of using dedicated “center-side” speakers. Indeed, some surround presentations are already mixed that way. My background is in television broadcasting where that’s quite common, though not universal. Having dedicated ”center-side” speakers as a sort of luxury seems to yield better results. I could speculate about a handful of reasons why.
I have also experimented with the center speaker of the tri-field array below the screen, but floor interactions drove me crazy. I’m less bothered by ceiling interaction, I guess. I even tried “over and under screen” centers with no ”side center” speakers with Magnepans and with the little JBLs. In both cases, disaster ensued, again probably for a variety of reasons.
Things are a lot easier with the box speakers because of their simpler constant directivity radiation geometry. Doing “anything” with planar speakers like Magnepans is challenging because room interaction is so hard to compensate for. Notheless, once I get all 9 of my Maggies factory refurbished and we’re moved into a new house, I’ll return to that love/hate relationship. This is a Dolby Atmos system, and the height speakers will continue to be Adam Audio T5Vs. I can only take on so much.
One more insight: if you’re struggling with just a single center-channel speaker integrating with the rest of your system, try this: spend a few minutes listening to “just” the center-channel speaker, everything else muted. Is the “image” truly centered and stable? You may find that it isn’t! If it isn’t, assemetrical room acoustics are screwing things up. I can’t emphasize this enough. Try to fix the room as best you can, and be aware that going to a tri-center approach does offer the means to fudge some compensation for the problems with level and EQ adjustments to the “side-center” speakers, allowing you to “steer” the phantom center image to where you want it to be. That’s the magic behind the illusion.