I am a Resolution Audio dealer. I have never heard the CD55, but I do have a customer who replaced his CD55 with an Opus 21 after doing a head-to-head comparison of the two over the course of a week. If I remember correctly, his initial impression was that the Opus 21 had much-improved bass over the CD55...then later told me that the Opus 21 was much better overall; more sophistication and refinement, etc.
He originally contacted me via Audiogon, so perhaps he'll chime in...
