i have listened to every one of r’ wallerstiens shiurim and he mentions non-jewish music in almost every single one but he did go into it more extensively in one shiur and it was incredible, really moving…but i dont remember wich one it was specifically, sorry. but really they’re ALL worth listening to. when u have a few minutes just downlaed it to ur ipod and listen to them while pesach cleaning. VERY WORTHWHILE i promise.