Do not confuse gain with power output. The Mission M778X has 31 dB gain, the Audiophonics has 25.6 dB gain. This means if you feed each the same input, the Mission will be louder. However, the Audiophonics is capable of higher output levels if fed more input voltage.
For example, let's look at feeding each amp 0.54 V which is the input sensitivity of the Mission.
Mission - 0.54 V input
Voltage Out = 0.54 x 10^(31 / 20) = 19.2 V
Power into 8 ohm = 19.2^2 / 8 = 46 W
Audiophonics - 0.54 V input
Voltage Out = 0.54 x 10^(25.6 / 20) = 10.3 V
Power into 8 ohm = 13.2^2 / 8 = 13 W
If you feed the Mission more than 0.54 V it will clip and not produce any more power, however if you feed the Audiophonics more than 0.54 V it will keep producing more power until you reach the input sensitivity of 1.66 V.
For example, at 1.01 V input, the Audiophonics will produce 46 W in to 8 ohm just like the Mission with 0.54 V input.
Audiophonics - 1.01 v input
Voltage Out = 1.01 x 10^(25.6 / 20) = 19.2 V
Power into 8 ohm = 19.2^2 / 8 = 46 W
To get 125 W into 8 ohm out of the Audiophonics you need to feed it 1.66 V.
Audiophonics = 1.66 V input
Voltage Out = 1.66 x 10^(25.6 / 20) = 31.6 V
Power into 8 ohm = 31.6^2 / 8 = 125 W
In case it isn't clear, to increase the input voltage to the amplifier you need to turn the volume on your preamp up.
Also, what are you feeding the preamp with? It looks like it only attenuates and does not provide any gain, so if you have a low voltage source in to the preamp you might not be able to get the full power out of the Audiophonics.
Michael
