Yeah, but still, if you want something that will show how well, or how poorly, your speakers can delineate different instruments, an ensemble of unamplified acoustic instruments, well recorded, would be better than Dark Side.
Maybe I am just a WYWH kind of Floyd fan. Dark Side lacks staying power for me. And I hear the same sort of distracting congestion in it too.
Anywho, back to the speaker end of the equation, I wouldn't junk your speakers based on their rendition of Dark Side. Those old Bostons were always easy on my ears, from what I recall. But there are undoubtedly better modern speakers to choose from, if and when you upgrade. But even, say, forum favorite Philharmonic BMRs won't separate instruments in the blob of a mix of DSOM any better.