Hi there. I've had both in my system and ended up with the Audio Mirror. If I had to describe the sound of each in a few quick words, I'd say the Amber 3 is bright, lively, and dynamic and the Audio Mirror is organic and fleshed out. I really like the AM. I would only consider the Amber 3 if your system slants towards dark and could use a bit of "activation" from the DAC. It was not a good match for my speakers which can be bright and revealing.
You can get both on home demo though, so direct comparisons are easy, minus shipping costs.
You can get both on home demo though, so direct comparisons are easy, minus shipping costs.