Plug in either or both to the Belkin. Cheap surge protectors don't have a high current draw outlet and can cause issues with high inrush products such as amps and subwoofers. But, the Belkin is made for A/V and is designed to handle high inrush products like the sub and the amp. If you only plug one of those two in, then plug in the amp, but I would plug them both into the high inrush outlets on the Belkin product.