It's a 100 dollar cheap dac that does not sound as good as my 115 dollar entire motherboard with onboard sound card. THAT is the issue. I did not expect miracles from it, especially given the sound quality that i'm accustomed to having at home and i most certainly expected it to at least somewhat outperform my onboard sound card.
No, they're not neutral. But I wouldn't say they have a frown frequency response. They don't emphasize highs, but they do plenty for the bass. I actually found the bass to be the strongest part of their response, and the most noticeable improvement.
I think it works great with Grados. Question: Are you running your headphones from the headphone jack? HeadphoneAddict once posted that it was the headphone out that's the colored part. You may like it more with RCA-out to the LD I+.
Unless I end up getting some Senns that need more power than the LD I+, then my uDAC will be the first component I upgrade. But I found it to be worth the extra $99 especially considering the dimishing returns of audio equipment. Not as big a difference as my headphone upgrade, but my headphone upgrade was three times as much.
Also: If you don't like the uDAC you may not like the LD I+. It's got a very tubey sound, which thickens up the mids. I found my SR60i almost unlistenable on it during a short test, probably because comfies thicken the sound already. Oh, and the SR325is is far from neutral. Fast, transparent, clear, but colored. If that's what you like and you don't want to sacrifice your bright treble, stay away from tubey tube amps.