Well, I have this card too, and it's a pretty nice card. I definitely could tell there was improvement. The first place that I tried it out was at work with my POS Dell CPx. In my opinion, Dell goes out of their way to make the sound on these as crappy as possible. I think it uses the ESX Maestro, and it is terrible. Upon putting the card into this Dell, I plugged in my DT770s and was greeted with...*silence* Whoa! Apparently, the Indigo also has an amplifier built in too. After reading the Tom's Hardware page, it appears that it's an Analog Devices SSM 2135. Overall, the sound is quite nice. It's perfectly silient and my DT770s showed that the amplifier helped. I now have the Indigo plugged into my META42, so the amp in the card just helps provide a cleaner signal to the META42.
I also tried this card out with my Apple Powerbook G4/667 running Mac OS X 10.2.3. It worked like a charm. I admit that the sound system on the Powerbook is a bit better then the Dell. I never really noticed large amounts of hiss, but the output was weak indicating a cheap op amp driving the headphone jack. No surprise there. Anyways, the Indigo worked like a charm in the Powerbook. The output was definitely improved by the strong output coming from the Indigo.
Overall, this little card is a very good deal. The output is great on it, and it does its' purpose well. It supports ASIO and GSIF output formats in addition to the normal WDM output in Windows. I tried using WinAmp with the ASIO output plugin to play some MP3s. It worked like a charm. I can't say that I heard any really difference in doing the ASIO versus WDM output, but I wasn't listening closely and doing comparisions either.
So, what are the downsides? Well, no inputs. Boo!! I have my Delphi XM radio coming into the line in on my laptop at work. I was planning to listen to it via the Indigo. That plan went down the tubes. The Indigo only cares about outputs, and only wave and CD audio output at that. No capability to use the line in of the notebook at all. My only other complaint with this card is on my Powerbook, you have to shutdown to eject the card. What a hassle! Echo knows about this problem though and is supposed to be working Apple to get it fixed.
So, in conclusion, I like the Echo Indigo and I would recommend this card to others. Just remember that not all laptops have bad sound, so your level of improvement could be minimal, or on the other hand, maximized!
