The 770 is specified to reach rated power at 1.4 volts, but that's probably 1db or more less than the amplifier is capable of. The Outlaw 770 is also rated for a gain factor of 28db (gain specs are usually pretty accurate), which is lowish for a home amp, though 28db is typical of unbalanced ATI-designed amps. (The 770 was designed and built by ATI.) Many home amps these days have a gain factor of 32-34db, because many receiver pre-amp outputs are weak (as are the outputs of my Outlaw pre-pro), and even ATI uses 34db of gain on the single-ended (RCA) inputs of their amps with XLR inputs too. (And the XLR inputs are rated for 28db.)
And sometimes just reading specs does you no good, even when you know what you're looking at, because manufacturers usually don't specify what impedance they measured output into. The Outlaw 975 pre-pro is rated at 2.0v RMS at the outputs, yet it can't drive my amp with 28db of gain to anything like full output. Go figure.
If the Denon drives your amp loud enough for you, be happy. Without a bench test you'll never know if you're really getting the maximum output the amp can deliver.