Do you have the same issue if you use the same amp but a different DAC? If not, I'd try that out first to pinpoint if it's the DAC or the amp.

If it is the DAC, then it's possible that you got a bad unit, so next you could try an exchange.

If you've confirmed that the DAC is indeed "working as expected" then the fact is that you just don't like the sound of this DAC (and don't let anyone tell you "it measures great so it must sound just as good as anything else").

This is what people mean when they say that DACs sound different, not that the FR produced by the DAC is incorrect, or that SINAD is bad (often they measure well by some measurements), but that there are other artifacts in the sound they produce that sound "unnatural" that are not part of any of the standard measurements taken. I wish there was some measurements that could determine this, but I have yet to see one. Objective performance should be used as a baseline for sure, but you still need to actually listen to it.

If you don't like it, return/sell it and get something that sounds good to you.