If you check my system page you can read a brief comparison of the momentum and the Ayre monos (should be similar to the S250, just more power).
I had multiple cases of the original Ayre (non twenty) mono main board going bad after about 1.5-2 years - it was a known issue that I don’t think they were ever able to get the bottom of. The twenty doesn’t appear to have the same issue since it doesn’t use the problematic component. I didn’t have any issues with my twenties but only had them for a year. On my M400s, one of the input boards went bad after about a year. My dealer got D’Ag to ship me a new one and they showed me how to swap it out which was pretty straightforward.
I had multiple cases of the original Ayre (non twenty) mono main board going bad after about 1.5-2 years - it was a known issue that I don’t think they were ever able to get the bottom of. The twenty doesn’t appear to have the same issue since it doesn’t use the problematic component. I didn’t have any issues with my twenties but only had them for a year. On my M400s, one of the input boards went bad after about a year. My dealer got D’Ag to ship me a new one and they showed me how to swap it out which was pretty straightforward.