The assumption here has been that matched gains are necessary or at least desirable. Why? The closer the match in gain, the better the common-mode rejection ratio (CMRR), which means those signal equal in phase and amplitude will be not be amplified as much as those in anti-phase. And as noise is usually a common-mode signal, the greater the CMRR, the quieter the amplifier.

The Problem
The Common Cathode amplifier seems to offer so much and  yet it is seldom used in audio gear. The reason is simple enough: the problem of DC biasing the two grids with dissimilar cathode-to-plate voltages. Remember, the current flowing through a triode is defined by the cathode-to-plate voltage and the cathode to grid voltage. If the first triode has a cathode-to-plate voltage of 300 volts and the second triode, 150 volts, then the first tube's cathode-to-grid voltage must be even more negative to lower the current through the triode to match that of the second triode. One solution, although not a desirable one, is to provide two power supplies: a 150 VDC for the first triode and a 300 VDC for the second triode.

The Solution
A zener diode with or without a bypass capacitor (bypassed would prove quieter) could be placed in series with the first triode's plate. An easier solution is to add an equal valued plate resistor as the second triode's to the fist tube, which can then be bypassed with a capacitor to the B+ connection or to ground. (Some do not bypass this resistor and thus lose the advantages of a low capacitance input because of no Miller Effect from the non-voltage swinging plate in the normal common cathode circuit. Additionally, the distortion is greater with the unbypassed resistor configuration.)

The Better Solution
The output impedance of the Common Cathode amplifier is roughly equal to the plate resistor in parallel with twice the rp of the tube. This might prove adequate for many circuit configurations, but probably not adequate for use as a line amplifier, unless a very low rp tube is used, such as the 6BX7 or 7119. Unfortunately, the low rp tubes are usually low mu as well.