Well, all the same speakers would be nice-to-have, but not if it is at the expense of a massive drop in SQ.
Depending on how loud you like your movies, the beds may really have to be SOLID, especially the front 3...
When I only had 3 B&W 803's, I was stressing the 3 7" woofers in the center almost to the breaking point, even though that speaker is ported to 28hz and rated for 350W. Hence why I build the center that I did (with matching L/R's).
Even though my SEOS's and mid-woofers are all the same drivers, bought all at the same time, there are still massive tonality differences between the 4 surrounds and the LCR; that's because the surrounds are using passive 2-way crossovers and the LCR's are active 4-ways (but the same drivers).
I also noticed that the tonality still varies even with the speaker settings are identical in every possible way and EQ'ed, that is because of slight differences in room acoustics, even though my walls are heavily treated at 50% coverage with an average depth of 4inches of absorption. Much much closer to an ideal-match though.
I'd imagine the only way that is going-away is if the room was circular and treated and lacking all furniture (or NOTHING more than seating at least) with all speakers at the same distance.
But circular and cylindrical rooms tend to (do) have HORRIBLE acoustics, so I'm not sure how well that would "actually" work out in reality...
Now that I actually have enough DSP horse-power, I suppose I could go active surrounds, but it's hardly worth the cost IMO.
The more I think about it, the more I think that a matrix plug in the back of our heads is the best way to go in order to trick all 5 senses with 100% precision, but until then, I guess 128 channels of Atmos is the "best we got..."
There are a lot of good sounding speakers but if you want great sounding or flawless, then things get MUCH harder and more expensive (and generally: bigger and heavier too...)
For male vocals you really need to be solid to 70hz at a minimum.
I've noticed vocal improvements even EQ'ing flat to single digits sealed, so sky's the limit.
Mid-bass subs are pretty much REQUIRED imo, without them drums and explosions just AREN'T the same,
hell even guitar rifts and pianos and a number of other related things.
Just like you wouldn't play pipe organ music or earthquakes or door slams and dinosaur stomps without dedicated ULF subs.
From a pure technical perspective, if you aren't flat from 1hz to 22.1khz (i.e. CD quality), then technically it is not TRUE hi-fi now is it? High fidelity STARTS with being able to play all frequencies, with authority and cleanly, and so pretty much ALL systems are a compromise to some-degree.
The question then becomes: when is good-enough good enough.
Some call it quits at 16khz and 15hz, others 20khz and 10hz etc.
The facts and truth is: Speakers and recordings will NEVER sound the same as the original live-sound that was supposed to be captured. For several obvious reasons: take a piano for example. That is a body that is large and radiates sound in all directions with mostly equal-power. That's not something a tweeter can really do, especially a domed or horned tweeter. So from the get-go you are already compromised. Furthermore, when we listen to such live-sound we are often moving our heads from side to side, even subconsciously, a static microphone isn't going to capture that, not even binaural microphones or other DSP trickery. Also most tweeters and mids (and even woofers and subs) lack sufficient dynamics to capture an aggressive piano hammering. Often times it clipped the mic and is thus clipped in the recording, or the recording is too soft or too muffled or was mic'ed too nearfield or too farfield. (There is almost no "good distance" to record at, only differences.)
It's hard to trick the human ear, we are designed to detect the slightest differences in level or direction or tonality or harmonic texture / resonances and distortions.
For these reasons and others, Humans can easily detect a real human singing from a played back recording, even on the world's best headphones or speakers. It is an exorcise in futility, but that never stopped us from trying regardless. hehe!
Sometimes you just have to kick back and have a beer, or 24... because, that's all that can be done about it.