To adjust your input levels, you'll have to do that before the signal hits your soundcard. There's a couple ways to do it, if necessary. Your tape deck may have an output gain control, you might connect the tape deck to a reciever, mixer, or preamp that allows gain adjustmets, or you might use an external A>D decive that allows you to set the gain. My suggestion would be an external device, like the M-Audio USB audiophile. The other advantage this has over the soundcard is I think less noisy and less prone to clicks/dropped samples since it's outside the computer rather than PCI card.