I had the same problem when I first got the Z1R, you can solve it with either EQ or a warm source. I've been listening to it with the DX300 with AMP12 and I love it. With the Hugo 2 and Chord Hugo TT2, it's best with EQ. When you EQ it or pair it with the right source, it is very hard to beat and certainly not at this price point.I got my IER-Z1R about a week ago. Loved it when I first heard it out of the box, it blew me away. I let them burn in for about 150 hours until I really wanted to start hearing my new purchase. I didn't think I would mind the "weak mids" myth, but mids are definitely weak. I was listening to an 80s song (I'll edit if I remember what it is) and using the Z1R with Apple Music Lossless/HIDIZS S9 Pro and it sounded like the lead singer was a backing track, could barely hear him.
I really like the bass and highs, plus the openness of the soundstage, but without some decent mids, I dont know if I can truly enjoy it. Been wanting to check out the U12t for a while to see if I like that sound better, but not sure if there is a way I can demo both the Z1R and U12t side by side (no decent audio stores within 6 hours of me).
I probably could fix the dip in mids with EQ, but with an iPhone, HiBy FD3 dac/amp 4.4mm port, and the Z1R, I haven't found a practical way to EQ on the go. I still plan on going through the systemwide PEQ on my Mac and running through Topping A50s/D50s 4.4mm port, but that really isnt a mobile solution.
Otherwise, punt and buy and Legend X EVO.