Hi guys and girls. My name is Jim and I have an audio system, amplifier NEC, two speakers and a subwoofer Yamaha YST SW215. First I connected my sub to my amp, the speakers to the sub and the amplifier to my external sound card on my pc. Due to the fact that the amp has a problem with the volume knob and you have to adjust it just the right way to have sound from both speakers and for fear of short-circuituing the whole system, I decided to exclude the amp from the audio system. So now, I have my subwoofer which has a built in amp and has its own power supply connected to my speakers and then to the sound card. But when I tried to play some music all I could hear was the bass of the subwoofer and no sound from the speakers. Why is this happening and how can I fix it???