Greg,
First of all I did say it "might" sound superior. I'll somehow assume your remark was not really meant to be a cursory or provincial bashing, nonetheless, I wish we all (myself included) would not have such polar opinions, or at least have them less often. You know, like the whole receiver vs separate amp thing. There are always some factors involved, right? Anyways, you also did notice that I always plan on having a center as well? It is true that the ideal setup would have one. However, pains sometimes must be incurred to get it right though, at least in some living rooms and/or AV cabinets.
-First of all, the vast majority of "matching center channels" are compromises in design with their horizontally arrayed mtm's. This creates off-axis issues with freq-response/phase/lobing. You sit front and center? Cool, then phantom might work too. The only brands that I can think of off the top of my head with top-mounted tweeters for the centers are B&W and Revel. There must be others, I just don't know them off-hand. See, the mtm is dispersing up-and-down, not side-to-side like towers would.
Then compare the "matching center channel" with the towers involved. Often, the "quality towers" seem to be of superior quality than the "matching center". Assumptions, perhaps, impressions as well. They often sound better, and the cabinets are sure larger.
Then look how many people have a dinky mtm center shoved into the cabinet, with all of its terrible reflections and resonances. Not allowing much in the way of disperion, and very possibly loaded with distortion. Im not saying always, right(?), Im just saying there are living rooms and AV cabinets out there that might cause such effects. Otoh, towers can be placed away from room boundaries (or boundaries of any kind, besides floor of course), corners, tv stands, whatever, for superior dispersion, response, imaging, whatever man. Having a center channel is very nice to have in order to center the dialogue, but I think my point was that some people never even considered phantom, when it just might actually sound superior. They could be completely ASSUMING having the center is ALWAYS best and never even gave it a thought. How many people buy 5 speakers, for say $1k? Subtract the center, you probably get an extra $300 to throw into the towers. Just possibilities, but I think they would be prudent to consider at least in certain situations.
So, money saved by not spending on the center channel can then be used for even better mains. And you know what, I find that center channels are normally over-priced for the quality received in comparison to their matching towers. They charge more because they can, because heck, its the "matching center".
I think its possible (especially for sweet spot viewers who have very nice towers) to get superior audio, if the alternative was shoving a dinky mtm center into a reflective AV cabinet.
If I ever upgrade/downgrade/change my horizontal center in the future, I will probably put it on a center stand. I don't want to deal with the looks right now. Mine fits just perfectly underneath the display, w/o blocking IR, yet it is surely still dealing with reflections by sitting on the cabinet, even if there is not a shelf on its sides, nor above it. I say this even if it protrudes from beyond the lip of the cabinet as well.
Of course, the best scenario would be to have 3 identical towers in the front. An acoustically transparent screen? My friend works for Da-Lite screens, and he say don't get it because the pq suffers in his opinion. What to do? Perhaps a top-mounted-tweeter center firing upwards from a center stand...... or phantom-imaging like some projection owners do, for precisely the reasons stated.
I was only throwing an idea out to be considered that indeed has some merit; its not "just silly".
Lastly, for those of you may try the phatom setup for any reason, aforementioned or not, it is most successful by avoiding a null spot. If your towers image very well, you are less likely to have issue of course. Otherwise, bringing the mains closer together will help. A compromise might be a smaller soundstage, but again, as always, it depends on your room/setup.
