I too have the same problem with iheart radio and tune in radio however, I think it is more a problem with the app/service itself. I use pandora more than any of my streaming services and feel that the quality is leaps and bounds above the rest... even with the free version of pandora.
I have noticed with iHeart and tunein the quality is usually around 44kbps (ACC) even with a solid connection. To me, it sounds like an am radio. I've looked in the settings for both and there does not seem to be a way to improve it. If I log in and stream either from my laptop, I seem to get the same results.