Cambridge Marriott, and the Residence Inn, which is one block from the Marriott, are literally across the street from MIT, 1/4 mile to the Longfellow, same for the nearest part of Memorial Drive. This is just north of the east end of campus. Once you’re out there by the river, it’ll be nearly impossible to not hear the music from somebody on the street. Most people listen to the broadcast from the Hatch Shell because the fireworks show is timed to the music. You might also consider bringing your own radios, or streaming app on your phones.

Do note that the Esplanade and Mem Drive in Cambridge gets several hundred thousand people for the show. Walking and the T are the best/only reasonable options to get around that day.