daltonlanny,
Glad to hear that the DT880/2003 are to your liking. I'm not sure what you are amping them with, but I really liked the '03 Beyers paired with the all-tube Darkvoice 336i.
Like you, I, too, owned the K701 on two, separate outings and, rec-cabled with RAL Paradise Cryo-Silver, they were actually my reference cans for over a year. The K701 have a disjointed smear/kink in their upper midrange/lower treble that reeks havoc particulalrly with vocals and makes the frequency transition on either side of it problematic, if not altogether impossible.
After I heard how cohesive the K501 were by comparison, with their ultra-pure, seamless midrange, I could never go back to the K701. I still own and very much enjoy the K501 (w/UP-OCC solid silver re-cable). As far as I am concerned, they establish THE benchmark for midrange reproduction within their price class, above their price class, and sometimes WAY above their price class.
While the DT880/2005/250 were a huge disappointment for me, I have found solace in the DT880/600. The DT880/600 seem to adequately address the midrange deficit of the '03 model, but at the same time retain enough of the HF and LF extension of the latter to produce a balanced and satisfying listen that still feels "in league with" or "faithful to" the '03's "house sound". Because of their more fully developed and better integrated midrange, the DT880/600 offer a dimension of tonal shading and dynamic contrast comparatively lacking in the '03 version.
That said, though, the DT880/600 do not offer that nth degree of frequency extension at either extreme which the '03 version generously deliver. For me, that is the bona fide "magic" of the DT880/2003, producing a very airy, often wildly expansive and enveloping listening experience unparalleled by any of the subsequent Beyer offerings--up-to-and-including, IMHO, the flagship Tesla T1.
In fact, I sold my T1 and kept the DT880/600 mainly because the DT880/600 exhibited a closer sonic kinship with the DT880/2003, while the T1 sounded, to my ears at least, nearer in essence to the DT880/2005/250, my least favorite of the last three DT880 iterations.
Anyway, enjoy the DT880/2003. No matter how you cut it, they are and ever will be true headphile "classics" in my book!
Cordially,
Patrick