If I had to recommend just one loudspeaker for adventure or scientific movies to be played on the Denon X3700H, I would suggest the Klipsch Reference R-51M. These bookshelf speakers are designed to deliver a powerful and dynamic sound, making them ideal for adventure and scientific movies. They have a crisp and punchy bass that will add excitement to your movie playback, and the detailed and natural sound will bring the movie to life. Additionally, the compact design of the R-51M makes them a great option for those who have limited space in their room.