£400-£500 upgrade (or addition) to the Amperior?

[Gofre]

Hi everyone,
 
So yeah, I've decided to finally get around to selling the headphones I've accumulated over the last couple of years and streamline my portable rigs down to just a couple of pairs. With any luck I'll get around £400 from the pairs I'm letting go. I'd like to either spend that on a pair of IEMs/CIEMs to use alongside my Sennheiser Amperiors, or sell the Amperiors too and get a new pair of on-ear/over-ears, so I'm looking for suggestions for both

In terms of sound signature, the Amperior and HD25 are the sort of sound signature that I tend to enjoy the most- relatively flat but punchy and with a nice sparkly treble. I listen most to metal and EDM and I'll be pairing them with an iBasso DX50. Any recommendations would be appreciated!

 

[Gofre]

Bump
 
I'm currently thinking of getting the NAD VISO HP50, having looked around I don't seem to be able find any significantly better pairs of over-ears that are properly portable. The rest of my budget can then be put into a pair of IEMs. Anyone have any thoughts? If anyone has any experience with the HP50s and the Amperiors to offer a comparison would also be appreciated.