I've narrowed it down to the DT770 Pro as my first choice, and the HD650's and HE-400 as my other options. I have demoed the HD650's and I like them for pop, electronic, etc. and they're warm and fun but I find them lacking in the mids and soundstage quite a bit compared to my 598's. So in this case, I feel like it can be a good partner. I can also get them for a cheaper price, around $370 USD here in China and I know that would be a great opportunity to own a great pair of headphones that can also scale up when I have more money because I hear they can go quite a long ways with you over time. I've also heard great things about the HE-400's and they sound like a sound signature I would like and it would be cool to own an ortho. Finally, the closed-back, bassier DT770 Pro sounds right up my alley as I hear the bass is prominent and nice and controlled. I may be able to demo the Beyers soon but I most likely won't be able to hear the Hifi's at all, anywhere near me so I would have to wing those. I'm basically considering these three based on all that I've read. The phones don't necessarily have to be the most neutral because I'll use my 598's for that stuff, they just have to be fun and right for the music.
Additionally, I'll be sourcing from my Lenovo and my DAC/Amp is a Fiio E17/E09K at the moment. I won't be upgrading those for a while but certainly will to some new Schiit in the future, so scaling up can be a consideration for your suggestion if you want it to be, but doesn't necessarily matter right now. I'll be keeping my HD598's and this new can for a while too.
Thanks a lot in advance!