whatever you do, don't use MUSIC to mask the tinnitus!!! adding noise onto tinnitus makes it worse in the long run.
While riding musician's earplugs might help you; but i've got to say; safety for me is #1 so even though cars are loud (and i ride in a busy high traffic city) there's no way i want my hearing muffled even a little bit.
the occasional car gunning his engine is probably not going to hurt you.

As for tinnitus, have you tried going a day with ear plugs in your ears all day?
(not on a long bike ride)
WHen I work in a certain lab, i was getting tinnitus and was able to pinpoint the cause to a set of loud fans. Earplugs made the ringing all night go away.