the 3001SEs and the original 3001s are very different speakers, the 3001s have more of a mid bass hump and sound darker. in fact the design of the 3001SEs were the basis for the Blade. I'm not a fan of the 3001s so much, but the 3001SEs are probably the smoothest most holographic speakers I've ever heard where in 3.x you'd swear you can hear above to your sides and even behind you while playing video games with surround or in movies. that being said, the t series are better for wall placement, the 3001SEs on their stands however especially complete with the 3001SE center (arguable the most versatile center KEFs ever made) is probably the most seamless and smoothest 3.x setup I've ever heard, I even did a comparison between the q150s here since those seemed to be all the rage at the time:
there's this velvety or buttery mids thing that the 3001SEs along with classic KEFs have that newer KEFs just don't and sound kinda hollow in their mid range which I can see how some people might mistake for "more detail" because it kind makes them sound more crisp but at the cost of midrange smoothness and tone. I listen to music literally from the time I wake up to as I fall asleep and so I obviously sold the q150s. What amounts to the impression of more detail is just playing with the same frequencies that cause nails on chalk board to cause pain. a bit of a dip there just makes for speakers you can listen to all day while your ears adjust and are invited to listen deeper versus having the "detail" firing at you.
the 3001SEs aren't bright speakers, they have a BBC dip and are basically tuned exactly to the default audyssey curve entirely on their own to the point where I don't even bother using audyssey on them, the only reason why you'd want it is to artistically remove the BBC dip midrange compensation. the thing with the 3001SEs is that they may not seem as bright and so don't seem as immediately impressive as the q150s, but after some listening you'll realize that the sound stage is just much deeper and 3d than the q150s. it's really the it smoothness, timing and holography that makes them shine, even if the t series might sound brighter and give you the impression of more detail, you don't get as much of the sense of space.
the t series are also not single point so don't have the same holography I e. timing as the 3001SEs. the 3001SEs also seem to be a lot more responsive to whatever you feed them just like the ls50s.
the 3001s and also some sketchy 3001SEs do seem to exist though if you try them second hand where it's obvious that the two speakers don't match when you play white noise and switch back and forth. if you have a set where white noise doesn't sound exactly the same when switching back and forth then I'd definitely switch them out because there's no way those are gonna sound nearly as good.
if you got them second hand I've seen some Frankensteined 3001SEs that don't match at all and some that even bottom out with audible distortion like the q150s and the e301s when played full range.
if you're into JBLs or klipsch the t series or even the q150s might sound better to you, if you are more into classic kef the 3001SEs seem to be the only speaker that literally rides the cusp and gives you both the mid smoothness and musicality of classic kef with the extention holography and high res almost ribbon like shimmer of new kef. the q150s and t series are completely lacking in the classic smooth midrange while the q150s like the e301s are surprisingly muddy when it comes to bass.
here's a tip play the 3001SEs full range or at least cross them over low at like 50-60. Their ability to generate stereo chest thump is something else they have the ability to do and completely cleanly.
if you are planning on selling your 3001SEs and you're the original owner I'm definitely interested in buying more. I've tried buying them off of ebay and was disappointed by getting a mismatched pair so now I'm paranoid.