Just use the boombox, hidden away somewhere, just make sure someone tests it first so they know it's loud enough and burn all the tracks on to one cd in order of when they're to be played. You can burn one CD for music while everyone is sitting/waiting. And then another with the ceremony music on it in order.
Of all the weddings I've been to, the ones with the processional music that stick out the most in my mind are the ones who used unexpected music or something very special to them. Like, Til Kingdom Come by Coldplay. That one was lovely. One of my friends used Such Great Heights by Iron and Wine which was just very much their style. Beautiful Day by U2 makes a great recessional, although it's been done a lot.
At my wedding, I chose to mix it up a little and used Water Music for the processional and then Kiss Me by Sixpence None the Richer for the recessional. We used music from Legends of the Fall for the time while everyone was being seated and waiting.
Don't feel restricted to "wedding music". It can be really fun to pick something that really means something special to you.