Start by e-mailing Craig at the address specified on the Whiplash web site and then take it from there. He is doing a dual entry hardwire to the drivers for me on the Ultrasone Signature Pro to balance them
I also find the DX50 screen plenty good enough for a dap. More storage is irrelevant unless they make it near 1TB as I'd still have to swap cards. Longer battery could be nice but as it is, it runs about the same time as my amp so still wouldn't matter.
In my opinion it makes no difference what so ever if there is one or two slots, no matter I will still have to swap cards. To avoid that it would need at least 1TB of internal storage which is never going to happen