I'm not sure if Ah has a volume control, but in every CD-player or DAC tube output is an inverting amplifier i.e. has no gain(i'd say has a negative gain more-likely). It introduces an additional local feedback to help to filter-out the digital noise and negate RF influence i.e. such tube output alone can only be a part of tube preamp(usually used as an input stage).
You should check-out the output impedance of CD-player if it less 8...10x than input impedance of your amp section and input sencitivity for a full output power also matches to approximately 70% of max output voltage of your CD-player.
You should check-out the output impedance of CD-player if it less 8...10x than input impedance of your amp section and input sencitivity for a full output power also matches to approximately 70% of max output voltage of your CD-player.