I spent less then $2 at the craft store the other night on some felt and tacky glue. Modified both the K550 and K701. It didn't change the character of the K550 too much but it added low end texture to the K701 that it previously lacked. I got my K701 used sans pads. Therefore I don't know if the K701 came with foam inserts for between the headphone and the pads. I'm not a bass head, I prefer bass that is accurate the recording and the felt inserts I made for my K701 have made these cans quite listenable for me with hiphop and EDM.
I still prefer the K550 on vinyl as I don't personally think the K550 is as source dependent as the K701 and my vinyl end could use some work for sure.
Thanks for all of the ideas K550 Appreciation thread!