Lon, assuming that there isn't a problem in the EP175 amp, the way to get enough signal to the sub to keep it awake is by way of the sub output level trim control on the 3805, not just by changing overall volume level. Increase the output level to the sub on the 3805(you didn't mention where you have it set)and to keep the same calibration for the sub level, reduce the level control on the sub itself a corresponding amount so that the sub doesn't get louder.

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Enjoy the music, not the equipment.