I think the 10/2 has a RCA "tape in" or something like that. I'd take a 1/8" stereo phone to L/R RCA's adapter and plug the 1/8" phono into the soundcard line-out and the RCA's into the "tape in" Your soundcard likely outputs at the consumer level of -10dB instead of +4dB the stereo channels are expecting, the "tape in" is designed for consumer level audio.