Just general info.
That’s funny.
The amp puts out about 45 watts RMS/8 ohms, and 75 watts/4 ohms. Overall gain should be about 26dB. This translates into 950mV RMS (or just under 1V RMS) for 45 watts RMS output into an 8 ohm load. Input impedance is likely to be nice and high to make it compatible to a wide variety of preamplifiers, circa 47K ohms or so (hard to be exact without measuring the amp).
This is similar to datasheet specs on the LM3886 chip. I would look at that to be honest as most manufacturers divulge little other than dimensions and weight of an amplifier.
Best,
Anand.