I'm Sick and Tired of the Lack of Rock and Metal

Just an idea - You could try to find songs in Simlish from previous series, like the ones @CK213 posted, to add to your 'Costum Music' folder? I personally preferred songs in 'hooman' when I had Custom Stations in TS2 (haven't gotten around to it for TS4, the only times my sims listen to the radio is for alternative or pop to increase the chances of getting a girl/boy), but having songs you like in Simlish could be a "meet me halfway" solution, until more genres will (hopefully!) be added.