Extremely low quality sound from audio channel

I tried to connect my digital piano to my computer and to hear it from audio channel in Cubase.
I connected the DP to the mic input of my soundcard, I tried to connect it from my DP line out R, after that I tried from line out L(mono), and also tried from my DP headphone output.
With all three possibilites I got extremely low quality distorted sound, and I could hear myself only from one side of my headphone.

How can I solve this problem?

The problem is the mic input, you have to go to the line input on the soundcard.

If the line in on the soundcard is a single connector, you need a cable with two mono connections for the DP going to a stereo connection for the soundcard.