6V is legendary line level output.
Anywho, the amp STILL works as hard as it would with a 2V set of preamps.. it still has to put out X amount of wattage for Y amount of sound. Since the gain isn't a volume, it's a control that balances the input voltage of the RCAs to the amp's output. That's why your gain is turned so far down, because the 6V preouts are super high compared to normal outputs.
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