Can't speak to the Icon, but I have both the Sigma and the Alpha, which are very close tonally, so close that I doubt your could tell them amart on casual listening. However the Alpha is better resolved, detail wise, and does a bit better at imaging. I also like the Alpha also because it has multiple selectible inputs and it has a sleep function - you don't have to go behind the DAC to turn it off, and its fast coming out of sleep when you turn it on, otherwise it takes about a half hour to warm up. The Sigma has a bit of transformer hum - the Alpha is dead quiet. At the prices I see on Audiogon I think the Alpha is a much better deal.
