I got the Shure SE535's for $350 on earphonesoulutions blackfriday sale so thats what I did, I beleave you can still get them for around $400
Your amp is fine it is what I have to, no other amp has a timer, eq, hold button and most have a volume wheel or dial that will get messed up in a pocket.
For over ears it depends on what you want id say HE-400's but I like bass, if you can get the HE-500's for the same price and don't mine a brighter sound why not? Idk if the E17 will drive them?
Theres also the Amperiors, Momentum, or try to score a pair of D5000's there my favorite right now