Sorry, I don't really understand your problem - you are using the CK100pro with the MDAC's front panel headphone jack?
The MDAC in standard form has a dynamic range of over 122dB, this puts it up with the best - I cannot believe that the CK100pro's work with other products yet have problems with the MDAC as few products reach 120dB dynamic range... for example the Iphone is less then 100dB (that's atleast x10 higher noise).
Unless your MDAC is faulty....
Headphone amplifiers have typically far worst noise performance, at the MDAC's 122dB dynamic range your approaching thermal noise limits (say at around -130dB for the absolute very best) this limit applies to both Digital or Analogue domain level control as the thermal noise is always present in the analogue domain.
As I suggested earlier your best option is to visit your dealer to see if he can advise you, or you can send your MDAC with the headphones to me in Czech Rep. and I'll test the system for you FOC.