You should really audition the Stealth M-21 special. I've compared it with Cardas Golden reference, AZ Matrix MKII, AZ silver reference, Audio Note AN-Vx Vz, NBS... by far this is the most musical in my system and in my other friend's system too. I place it between CD player and preamp. 30 days free trial. You should really talk to Serguei from Stealth Audio.
Cardas Golden reference -- dull
AZ Matrix MKII -- lack of good detail, poor low freq response
AZ silver reference -- good detail, punchy, poor low frequency response
Audio Note Vx -- musical, a little constraint in upper mid but still better than Cardas and AZ.
Vz -- musical, bigger sound, slight colder and brighter
Stealth M-21 special -- good detail, punchy, excellent bass control, very musical, big wide and deep sound stage.
Nothing negative to say about M-21 special.
This is not the same as the regular M-21. This was made under my special request.