The maximum allowable bitrate for video+audio+subs on a DVD is 10.08Mbps. From what I gather about Muxman, it can deal with the occasional spike above this value, but any sustained excess will cause the muxing operation to fail. (Which is a good thing, because playback of such a disc would be problematic on some DVD players).
So yes, in your case you will need to compress the audio to AC3 or MP2, or encode the video again using a lower maximum bitrate.