Open back over ears VS CIEMS

I've wanted a pair of CIEMS for quite a while now but the release of the HD6xx has got me wondering what is so good about higher end OEMS that people forfit the convince of IEMS for ?
The big problem for me as a student is that so much of my listening is done while traveling and studying etc where I am unlikely to have as easy access to a AMP/DAC and or my headphones may be disruptive to others. although I do offen make time private listening it is not even close to being the majority of my listing time.
so what are the pros of over ear open back headphones and or cons of in ear . and just how much better a listening experience would they offer when when paired with a good DAC/AMP.
any experiences and advice is much appreciated
Thanks in advance
100% upvoted

Nov 10, 2016
If I am alone in a quiet room, I almost always choose open-back headphones. They sound more open and more natural, IMO. They avoid the minor-but-real discomfort of being isolated, too. At home I usually use Hifiman HE-560 headphones.
At work, I have to use IEMs or closed-back headphones so that I don't disturb my co-workers. I usually use closed-back over-ear headphones because they are 1) visible, so people know that I can't hear them if the walk up to talk to me, 2) easier to put on / take off when necessary, and 3) generally more comfortable for me to wear for hours vs. IEMs, though I can imagine that is a personal preference. At work, I usually listen to Fostex TH-X00 headphones.
On airplanes, buses, or whatever, including when I walk to a cafe for lunch during my workday, I usually use IEMs because they are easier to bring with me. I have a bunch of IEMs scattered around in different places. The ones I use most often are Final Audio Design Heaven II, LH Labs Vibrato, JH Audio JH-13 Pro, and Zero Audio Carbo Tenore and Basso.
Whatever your requirements, there are headphones (and amps, if you want an amp) to meet your needs. Personally, I enjoy trying different headphones and related gear.