Astav, you didn't identify the sub, but any sub with its own amp doesn't receive any power over either the line level or speaker level connections, so the cable(unless it was totally broken)shouldn't be the problem. I assume that you tried turning up the level control on the sub. If the added voltage using the Y-connector helped, then you need still more voltage from the sub output on the receiver. I'm not familiar with your receiver, but any receiver with a line-level sub output has to have a provision for changing the level of that output. The owners manual should at least briefly discuss the point.
