Balancing Amplifiers  / & DIM Switch
If you have two different kinds of power amplifiers and want to use them both at the same time, but they supply different amounts of gain, what do you do?
One solution is to add a little bit of attenuation to the input(s) of the amplifier which has more gain than the other one.
This is accomplished by inserting a simple two-resistor voltage divider between the amplifier's input RCA jacks and the amplifier's input circuitry as follows:
You should first find out what the amplifier's input impedance is. After that, you may have to do a little bit of experimenting to determine exactly how much attenuation to give the amplifier. Usually, about 5 to 10dB of attenuation added to the higher gain amplifier is enough to match it with the lower gain amplifier.
The following tables show the amount of additional attenuation provided by different  R1 / R2 resistor combinations - for use with amplifiers which have specific input impedances. 

DIM Switch

This circuit  shows a resistor voltage divider which can be used to attenuate an input signal to a piece of gear or a set of amplified speakers. Depending on the resistors used, you can attenuate a little or a lot. You can use the resistor values shown above, which are chosen according to the input impedance you would be connecting the output of the circuit to.
If you choose to attenuate a relatively large amount, say, around 20dB, voilą, you get what is called in recording studios a DIM switch.
Shown above is one channel only - on a single-pole double throw switch. So for stereo, duplicate the circuit using a double-pole switch. For balanced stereo, you duplicate it four times, using a four-pole, double pole switch. We drew this using a toggle switch. But you can use a rotary switch instead if you want to, of course. The Goldpoint high quality rotary switch part number you would order is 4P-2T-1D.