I ran a MF M1 HPA for some time, really liked it as intended and used it as a single line pre amp. The BM2 bettered it with my 650s, almost as if it had been tuned to suit the Senns.
The Capella surpasses the sonics of the BM2 offering a noticeable upgrade. As a pre amp it has displaced my Tisbury audio passive. What has surprised me is how effective it has been in getting the best out of my other headphones- Superlux various models. I rarely used them because the 650s were so much better but now I can tune the Capella to match the needs of the other cans. I am now seriously thinking of expanding my cans collection....maybe a cheeky pair of beyers might find they're way into my christmas stocking!!!!!