Didn't we have this same post in November? It's a fine AB amp, inexpensive, owners like it (I do), the reviewers like it. Unlikely anyone will be able to comment on it vs the Sigma or with your particular speakers, that's a needle in a haystack. Talk to Walter at Underwood, he will have the most info, not sure if he has anything to demo, that's the challenge with smaller brands with limited distribution.