Getting the gains set appropriately in the various parts of the signal chain is important in order to avoid distortion and clipping at higher signal levels and to minimize noise at lower signal levels.
With Marantz pre/pros, this concern has to include the trim levels on each of the inputs (which can be set individually), the trim levels on each of the speaker channels, and the setting of the master volume control.
If you can avoid it, you shouldn't try to compensate for low gain in a later stage of amplification by increasing the gain of a previous stage. When carried too far, this can cause the output of the earlier stage to overdrive the input of the later stage, which results in clipping. This can have audible results (a harsher sound) and, if the clipping happens in the final amplifier stage, it can cause damage to speakers (due to overheating by higher average currents through their electromagnets).
I'm surprised that you can't run the Crown amps with a gain of 100% without audible noise. Are you hearing that with shorting stubs connected to the Crown amps' inputs? I.e.
with an input signal guaranteed to be 0 volts with no noise? If so, I'd contact Crown, since the spec sheet for the 1500 claims that the noise is supposed to be 103dB down when driven at full power (i.e.
with an input signal of 1.4v rms). That should translate to being completely inaudible when the input signal (and thus their output power) is at minimum (0v) unless you have your ears very close to the tweeters.
If you're only hearing noise when other equipment is attached to the inputs, then the noise probably is originating elsewhere, and not internal to the Crown amps. You should determine if the source is internal to the amps by putting shorting stubs on their inputs: if the amps are essentially silent with them attached, then the noise source is external. (Due to a "ground loop", in the 7701, or elsewhere.)
Are your Energy speakers actually RC-10s? I can't find a model C-10 on their site. If so, bear in mind that they have a maximum power capacity of only 175 Watts, so driving them at the maximum possible sound level (with the Crown amps outputting their full 300W) is likely to damage them.
WRT the volume setting on the 7701, don't forget that after Audyssey calibration, the 7701's volume settings are logarithmic. They tell the 7701 the sound level that you want to have at your primary listening position. Its volume settings tell you nothing whatsoever about what fraction of their maximum power your amps actually are producing. In particular, a value of 80 on the 7701's "absolute" volume scale would make your audio system attempt to produce movie reference sound levels, with peaks of 105dB. Energy RC-10 speakers aren't quite efficient enough to do that, and would be damaged if you tried. However, in most home listening environments, most people prefer to listen about 20dB below reference, with volume settings in the vicinity of 60.
Harman/Crown provides a calculator which tells you how much power is needed to produce a specific sound level using speakers of a given sensitivity at a particular listening position. It can be quite helpful in evaluating the kinds of equipment to get if you want to be able to listen at full movie reference levels. See http://www.crownaudio.com/elect-pwr-req.htm
I hope these comments help a little.