I know the adapters for the Sonys for the IP bus are very expensive (100$) but I would go with that.
and Fm-modulator has a suprising amount of crappiness. Some people say they don't (but they must be already half-deaf from there loud music).
They sound about like someone stabbed all of your speakers with a screw driver. It is insulting.
And the adapter is not much more than one anyways.