A friend did me a super solid and picked up a pair of K501s for me at a killer price. I'm gonna pay him back plus $20 for his time on Thursday. I've wanted a pair of K501s for seven years or so. Like all of my other AKGs he finds them a little dry. When I see him on Thursday I'm going to loam him my bass moded Q701 and my K401. The 401 has a little more low end (so they say) than the 501, but at the expense of performance in the mods and clarity. He has Shure SE 215s and Jaybrids Freedom X3s at the moment. I think I'm the future the HD650 would be a great can for him to go with for at home listening. I know in the meantime he'll appreciate the clarity and detail of my AKGs. He's already texting me on a nightly basis now telling me what he's listening to on the 501s and how it sounds.
On the iPad Pro through my Sony XBA-4 in ear phones, streaming through JRemote from my media PC, sounds really good well balanced with great punchy bass. Cool looking balanced armature phones too, see review at https://www.head-fi.org/f/threads/review-sony-xba-1-and-xba-4.632053/
First time listening to this guy, so far impressed