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I don't think you 'broke' anything. But what input did you connect the subwoofer to, perhaps?
Connecting two inputs to each other usually won't harm anything.
No, you didn't burn up the speakers that way, that's impossible I'm certain.
Let me thoroughly look through the information on your Roland piano, and see if there's some selection you need to make to activate the speakers as the output.
Meanwhile, try turning up the Volume control for the speakers. If it is at a minimum setting, then no sound will come out the speakers... it's just a thought.
OK. Now the info on this digital piano is, that its internal speakers are very loud at maximum, so be sure to turn them down a bit again!
And what it says about the subwoofer is simple: it adds bass resonance. So it isn't an option that turns Off the speakers at all.
Did you ever hear anything from the speakers, since you got this Roland piano?
I'm sorry to hear that.
Try turning the Roland piano Off. Unplug it.
Leave it for at least 1/2 hour that way to cool off and reset thoroughly.
Then see if you can get it to work again without the subwoofer connected at all.
(What subwoofer model is it?)
How did powering the Roland piano Off for a while affect the problem (if at all) ?
I was wondering if something like that might be the case. But good. Glad to hear that a solution was found by whatever means.
Does this conclude the case?
If so, would you think my efforts were worth rating?