Did a short bit of DAP comparo with my friend today. I liked the X5 (though it didn't like my microSD card), but I'm still partial to my DX90. I think the jury is still out for him.
Mine: iBasso DX90 -> plusSound X Series -> InEar SD-2
His: FiiO X5 -> Brainwavz R3
Purchased from this seller on eBay, see description there for more information. Unused, I purchased one pair of size M and one pair of size L and the size M fit perfectly, so I don't need these. If you have an unused pair of size Ms, I would love to trade.
I just want to commend Christian on his amazing customer service. He was very quick to respond to all my emails even on a sunday night. Also a bit of advice for anyone looking to purchase one of the X Series cables: I think he uses the same wood slider for all of his cables, so the diameter of the hole is a bit too large for the X's thinner wires. Not a very big issue but if you need the neck slider functionality I'd recommend the heatshrink slider instead.