I think you hit the nail on the head regarding the T2 Plus. Objectively speaking, there's nothing offensive or "wrong" about it, yet they gradually became increasingly underutilized in my collection.
With the PortaPros, perhaps there was a mismatch between what it was and what I expected it to be. At the time I was running them out of my NW-A55 Walkman, so there may well have been a synergy issue as well. I have certainly not ruled out trying other Koss products though!
I do gravitate towards a clean sound with detail, resolution, sparkle and "air", with a realistic timbre for acoustic instruments. Not sure if that qualifies me as a treblehead, but it probably explains my picks right there
Try the KSC75, you be surprised on how different it is from the porta pro in both profile and quality.
yup, if bright, sparkly, and airy is the keyword, KSC75 is the better choice than portapros. also if you like to venture to earbuds, there's also Edifier H185 that shares similar signature as the KSC75. i personally prefer it more than the KSC75 though as a whole package, as it's also cheaper, and because the easier fit, have a more solid bass response than the KSC75.
finding that kind of signature on IEMs is a bit harder, especially among budget ones.. there's the original T2 (which you might already tried?) but still a bit different kind of air and sparkle than the two above