Talking about Marantz support, I can give you some information, which confirms what Gene DellaSela once mentioned about audiophile product manufacturers. In the past, they were providing more info on the specs of what they manufactured.
I once asked Marantz to provide me with the damping factor at 4 ohms for the power amps on their SR5010 AV receiver. They refused to give me the info. The person wanted me to believe that they never tested for that characteristic on their products, my ass!
Afterwards, I asked them to provide me with the maximum output voltage of the preamps on the same AVR. They only replied that it varies between around 1.5 to 2 volts. They did not have it as a set number!
I know that at least one of the previously released Marantz AVR had pre-out voltages exceeding 7 volts.
Would someone have more precise info on that receiver in this regard?