Ordered the RHA M750i and they arrived last night. Here are my initial thoughts:
Build/Design:
The build quality is top notch. The cord is thick, but there is zero feedback when touching it or having it brush up against stuff.
Right above the plug is about an inch of winded wire to help prevent bending and breaking. Not to mention the solid build of the jack itself.
Tons of tips, unfortunately silicone tips have always bothered me. The foam tips that came with them are stiff and a bit too big. So I'm happy I got a pair of Comply's when I ordered them. The mediums are fitting pretty well.
Music:
I skipped my amp with these (Schiit Magni/Modi) as I'll be using them mostly while on the go (phone or laptop on the train) and so far am really impressed. A good amount of bass, but still incredibly clear and detailed. I was a bit worried they would be really bright based on some reviews, but compared to my A151's they're incredibly balanced.
Fleetwood Mac's rumors is sound really nice right now. Everything is clear, detailed and Lindsey Buckingham sounds great.
As for something more modern I like to use Jessie Ware as I think her production is top notch. There is some low-end, not as much in my DT770 but it's there. With this I'm finding these to be a bit too bright but there is still a good amount of detail.
As of right now, and just 30-45 minutes of listening, I don't think I'll be disappointed.