I've written a few essays on sound design for uni, so i feel your pain. There's not a lot of theory out there, i guess because sound design is a relatively new art form, and practitioners tend to be very pragmatic. There is, as you found, some material out there concerning the horror and thriller genres, as they're very affect driven, and sound often contributes in a very overt way. For comedy and romance, sound devices tend to be less obvious, and are far more context dependent than genre dependent, so they're not as easy to write about.
I'd recommend scoping out designingsound.org for some interviews and articles by sound designers. I'd also recommend AudioVision by Michel Chion for some interesting definitions of sound devices (it also makes for a good bibliography reference, if your report requires that).
I hope that helps!