Portable Audio Upgrading? (FiiO Q5s and beyond)

[stonefields02]

I currently own a FiiO Q5s alongside a pair of KB Ear Believe's using 4.4 balanced on my phone and was wanting to go further down into the rabbit hole and see what I could do to upgrade my little setup, whilst still keeping it relatively portable. I've looked into the YinLvMei m400 and m400 pro, and while these seem like amazing devices they are out of stock and have been so for a while. I've also considered upgrading to some Mangird Teas or other planar headphones and so that leaves me with the question would it be wise to upgrade to a better DAC/AMP combo like a m400, another stack, or simply adding something else on to the q5s? depending on that what what would be a good next step? Would I receive more of a return simply upgrading my headphones? Any advice or recommendations are welcome.