If the 598 is bumping into your ears inside…you probably won’t do too much better with the DT770, I’m afraid. :(
They’re about the same as far as depth of the cup goes. The 770 has two small advantages. First, there’s a really thick layer of foam inside over the driver if you do manage to bump into them. Secondly, the 770 also has slightly stiffer foam than the 598, for isolation, but it’s not really any deeper.
As far as the connector goes, the 598 has a removable cable, so you might try an aftermarket one? I had a NewFantasia cable for mine that I really enjoyed, and it had a smaller plug on the headphone end. Cost me about $13 from Amazon, if I remember right.
Sorry I don’t have better news!
I re-read this article after you commented, and I’ve definitely become lax again on pads bumping into my ears…though I still love the space I have with my 770’s.