Maybe you should try installing that other driver anyway (?) Maybe you can only do either midi or audio via USB, not both at the same time? Dunno, I don’t use USB for much aside from powering devices, or USB hard drives, too finicky. That’s why I prefer standard midi connections for midi, you just plug it in and they always work! USB midi doesn’t always get recognized or get’s disconnected. For audio, analog line or digital connections are more reliable in my own experience. I tried using my midi guitar controller recently via USB after I had been using the regular midi out for a while…it worked once before, but I couldn’t get it working again 
As for distortion on the audio line outs into your sound card, you must have levels set too hot somewhere, check them at all stages…from out of your keyboard, in your sound card control panel and in Cubase etc.