I would start with a recording of good singers recorded by good enginners,say Maria Callas or Deitrich Fisher Discau(spelling) or the Robert Shaw Chorale,to see how much of it is the other recordings you are playing and how much of it is your system.
I suspect the recordings are the culprits but can't say for sure since I've not heard your system
I suspect the recordings are the culprits but can't say for sure since I've not heard your system