Hi, My guess is that you have 8 Ohm phones plugged into a 600 Ohm LINE OUT connector. Sound cards used to have 8 Ohm to drive bare speakers, for a time had both Spkr and Line out and now have only Line Out to drive amplified speakers. You will need an amplifier. Some speakers have an EarPhone Jack and turn off the speakers when the phones are plugged in. Good Luck, Jim