I’m just down to a DAP and looking for a good headphone pairing. Sold everything else.
Maybe add a C9 to widen the field of options?
I can only speak for myself but with the Max as with everything else, you'll get a range of opinions as to how it performs with... well anything.
But I was looking for a truly transportable all in one, had the DX300 and other iBasso DAPs as they provided the best amps for the most part for DAPs, and nothing has bested the DX300 Max for me given that use case.
I owned the C9 and the Phatlab Sassy GT as portable amps, for reference.
I paired the DX300 (non-max) with the C9 and did not find it to be a step up over the Max - it sounded a bit too soft overall without really being soft due to a tube-like tuning or anything from the C9. Just didn't sound as dynamic, to me. Yet I know the C9 does have a wee bit more power than the Max. This pairing it with the ZMF VC (and all other impressions I mention in this post).
I actually preferred the Sassy GT and found it to have more juice than the C9 despite the difference in output power on paper - something to do with how the amp itself is set up, but my impressions were matched by having the volume of the GT set to 10 o'clockish for the GT vs noon+ on the C9 regarding juice. Tonality wise I thought the GT had better dynamics while also being more tubey, though the C9 edged it out in staging width, whereas the GT was a bit more center-focused.
That said none of them were a true improvement over the Max as far as how well I felt they could drive the VC.
I also had the Empyrean paired with the DX300 and the C9, and while it drove it fully well I just didn't love the Empyrean's tuning overall - ZMFs just nail that natural, organic tuning without sacrificing detail or dynamica far better than the Empy can, IMO.
I think one option for you to try with the Max, if you don't like how it pairs with your ZMFs, is the Rosson RAD-0, which might be easier to drive and is akin to ZMFs in planar form as far as tuning.
I have not heard the RAD-0 so can't comment myself but Tyler's Ecletcic on YouTube recently did a review of them and he's a big ZMF guy, so his comparisons would come in handy. There's also a RAD-0 on sale in classifieds right now (be warned the impressions I've read are largely extremely positive for SQ but very negative for comfort, aside from a mod thaylt a fellow HF'er can make, apparently).
I know I've given you a lot of feedback on the Max and it seems like you haven't found what you're looking for yet - I'm just sharing what opinions I've gathered so far as we seem to have a similar goal and I've tinkered a bit in trying to find the best solution, so I hope this helps!