First you say “it’s the same” then later admitted “it can be better - if spend more”.
And your title “Wanna take it to the next level? Buy MORE speakers” implies improvement for surround speakers vs 2 channel.
Surround “envelopement” and “fidelity” are two different objectives- one is NOT objectively (factually) better, but you may have personal preferences favoring one
Stereo and multichannel have the same sonic goals, in essence, w.r.t how a soundfield, spatial cues and detail are offered to a listener in a room... except stereo gets there half baked, multichannel optimized for music gets a whole lot further. It is not really a preference thing.
You see these manufacturers trying different tricks... putting additional tweeters behind their cost no object speakers, etc? (except speaker shall only be a measly 100k now)...Or that fpga code magic in some 70k dac to unlayer, unfold, create spatial cues, better detail, etc better than ever? Why do you think that is? If the number of speakers remains restricted to 2, well, it is only able to get so far. Even a mediocre horse could pull a carriage further than a super cadillac dog...
I said my multichannel rig can run circles around my own stereo rig (which costs magnitudes more) and beats out any cost no object stereo rig i’ve ever heard. In other words, i didn’t even spend that much on my multichannel rig and it is able to do so. Could it get beat by some guy’s cost no object multichannel rig? Maybe, it could.. I did hear a very expensive multichannel rig set up by Anthony Grimani/Grimani systems once in a huge room that blew everybody’s socks off. Maybe...his multichannel setup did a li’l better than my multichannel setup in that large room....But, the case remains that i’ve always been let down by all kinds of cost no object stereo rigs i’ve heard.
For example, let us suppose that a guy already has a pair of Mofi sourcpoint 8s or Borresen X1’s and 2 subs...These are high value, but, not very expensive speakers. All he would need is three more sourcepoint 8s or three more Borresen X1s, 3 additional channels of amplification and a processor worth its salt. I would prophesize that such an exploration could provide a much better outcome at a lower cost..... than the guy ditching his Borresen X1s altogether and buying a pair of Borresen M1s for a 100k instead (i.e., sticking with some stereo only upgradititis).