I don't know if there's something wrong with my amp bit I think that the speakers sounds like a heavy load and that the sound isn't as "light" as I would prefer.... The speakers are connected with Supra swords and paired with an velodyne dd10.Can you describe how the sub is connected to the amp? The main reason I ask, given that your sub appears to provide speaker-level as well as line-level inputs, is that a common mistake is to connect the negative speaker-level input terminal of a sub to the negative output terminal of an amp having balanced (or bridged) outputs. That could very conceivably cause the symptom you've described, as your INT-150 has balanced outputs, and hence its negative output terminals provide signals and should not be connected to the ground of a sub.
Regards,
-- Al