I've had my Eureka for 7 or 8 months now. I've got to say, at first I wasn't particularly impressed with it for anything but Bass DI (which it REALLY sounds good at). In fact, the only reason I really kept it around was because it sounded so good as a Bass DI. Plus, it had a pretty nice transparent compressor and EQ.
But....
After using it on everything from vocals to kick drums, I have really come to appreciate what it can do. The adjustable mic impedance gives it a TON of flexibility. That one thing is the key to Eureka sounding really good, or really average. On a dynamic like a 57 for vocals, the more you crank up the impedence the "glassier" the vocals get. Turn it down, and you get a deep "movie announcer guy" kind of sound. But the key is, you need to test different impedence settings whenever you switch mics (dynamics at least) because you can get vastly different sounds on vocals and even electric guitar.
I kept it around for bass DI, but I have come to really like it. Believe me, I don't get attached to gear. If I don't like it after I have given myself time to REALLY test it, I will chunk it. I have bought and sold lots of preamps, even focusrites in a similar price range that weren't keeping around. To me, the Eureka is better than just anything I have tried in that range, when you consider sound AND features. If I find something better, I will chunk it. But for now, it is working out for me pretty well...
Here is a track I recorded with the Eureka on vocals:
