I was in a similar predicament a couple of weeks ago. I had two options: SR225i naked, or SR80i + uDAC. After much contemplating, I decided on the latter setup and couldn't be more happy. I'm new to the whole head-fi thing, so my virgin ears are quite pleased with the "low end" sound. Plus, I figured I could always add another pair of headphones down the road and keep the SR80i's for a set of portable/backup headphones.
As for the uDAC, I think it pairs nicely with these Grados. It didn't change the sound signature much (if at all), and really cleaned up the midrange as well as minimized some of the distortion at the extreme low/high ends. Needless to say, I don't regret my decision to purchase these two items. Pretty amazing quality for <$200.