tube ringing?

Hi folks, recently I replaced my Accuphase preamp with a CAT SL-1 Signature Mk III. My power amplifier is a Gruensch CSE II se and speakers are Soundlab A-1's. Speaker cable is Cardas Golden Cross. First I have to say that I hear a significant improvement over the Accuphase and I think it is a matter of pre/poweramp matching. The sound is quite good now but... with female voices for example Barbara Streisand I hear that the 600-800Hz region is emphasized. It reminds me of some ringing. Could this be ringing of the tubes inside the CAT? Or is it just room acoustics thing?

Chris