Best to find out where the overload distortion is coming from. There are two possible places and you are probably overloading at both.
Guitar into a soundcard... MIC input or line input? You would be overloading the soundcard (mic) input. Try setting the guitar output very very low and listen on the monitors.
Boss DS-1X effects pedal is -20dBu in and out. A guitar is a much lower signal (than soundcard out) , which is what your Boss DS-1X effects pedal is expecting, than a PC sound card which has output line-level, -8dBu or 0.316V AC, which will overload the Boss effects pedal input.
I would run the guitar first into a pedal/pre-amp to get the signal up, then feed into the PC soundcard line input. The MIC input is too sensitive and noisy.
Then, the PC soundcard output is too much for the Boss pedal, but Boss has a level control which might cover that or not depending on Boss's circuit inside.