Guillermo, you said that one way to rouse it from its slumber was to set the receiver volume "too high" and also that you've "tried playing" with the receiver sub output level. Unless the sub auto on is just plain defective(possible) and wasn't corrected the first time, it would seem that setting the receiver sub output higher to get more voltage out and compensating by setting the level control on the sub lower than the middle should work(unless you mean that you already tried this).

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Enjoy the music, not the equipment.