At the risk of sounding like a non-answer, I agree with the sentiment to consider the front end before the dac, although the improvements can be dac-specific, and it honestly depends so much on the level of the rest of your system.
For instance, if using USB, consider a better usb cable, a reclocker like an iso-regen, some linear power supply upgrades for anything in the chain not using them, and power supply improvements in general (balanced power or well-reviewed filtering). Sadly, any dac upgrade may not be as noticeable of an improvement without a lot of that already in place. This takes a lot of research and a lot of experimenting, but the yields can be significant. Read as much as you can. Try them one at a time, but some won’t yield improvements unless in conjunction (linear power supply combined with reclockers, for example).
I use an Yggy with a lot of SoTM, Uptone and Sonore network and USB gear in front, and the gains have been very significant, but the costs have been too. I had an Aqua Formula for 3 weeks, but by itself, it wasn’t a giant improvement over the Yggy plus upgrades (the latest with analog 2), although it would have been better likely with all those other upgrades in front.
just suggesting the dac upgrade needs to be considered with the other opportunities.
