What 12AU7 tube do you have in your CD player and have you tried other brands? The most dynamic 12AU7 type tube I tried with a Unico integrated amp when I had one years back was a 1965 vintage Radiotechnique. Very tight and deep bass and also very detailed in the midrange with an extended top end. Not a romantic or warm and mellow sounding tube. Other preferred tubes in this application for a CD player have been the Amperex 7316 and Telefunken 12AU7.
Experimentation with tube dampers such as the ones made by Herbie's Audio Lab could also be beneficial. My experience with these in a similar application is better focus and soundstage, deeper and tighter bass and a generally smoother frequency response. Results may vary. Herbie's products have a 90 day return period so if it doesn't achieve the desired results it can be sent back.
Experimentation with tube dampers such as the ones made by Herbie's Audio Lab could also be beneficial. My experience with these in a similar application is better focus and soundstage, deeper and tighter bass and a generally smoother frequency response. Results may vary. Herbie's products have a 90 day return period so if it doesn't achieve the desired results it can be sent back.