I've compared it to the Electrocompaniet EMC-1 Up. I have both; the Opus 21 is in a headphone system; the EMC-1 is in my main system. I've compared the Opus 21 in my main system and here's a summary of my thought...
The Opus 21 is more "organic" than the EMC-1. It's more dimensional. It gets my foot tapping. In the "listening from the next room" test, the Opus 21 sounds more real, more authentic to the instruments. I've also run the Opus 21 direct to my Mcintosh amp and compared this with running thru my Mcintosh preamp. Without the preamp it sounds even moer alive and detailed. But with the preamp it sounds more dynamic, more alive. i think I prefer using the preamp, but it's close.
The Opus 21 is more "organic" than the EMC-1. It's more dimensional. It gets my foot tapping. In the "listening from the next room" test, the Opus 21 sounds more real, more authentic to the instruments. I've also run the Opus 21 direct to my Mcintosh amp and compared this with running thru my Mcintosh preamp. Without the preamp it sounds even moer alive and detailed. But with the preamp it sounds more dynamic, more alive. i think I prefer using the preamp, but it's close.