Must I repeat the make-up fasting for days I intentionally broke during Ramadan because I committed certain forbidden acts while fasting, or did not feel the hardship of fasting?

You are not required to repeat the fast of the days you have made up. Listening to music and looking at forbidden things are sins that may diminish the reward of fasting, but they are not among the things that invalidate the fast and necessitate making it up again. Similarly, excessive sleep does not invalidate the fast. We advise you to fear Allah and to complete the remaining make-up days and preserve them from anything that might tarnish them.