The N9 Wikipedia page says that it has "a speaker". This is consistent with visual reports of the N9 having only 1 speaker opening.

Since the reason I bought the N900 was to consolidate devices in the best package, & the N900 had stereo audio playback, the N9 is less desirable.

"Use headphones" is distraction from the fact that playback without headphones on the N9 is monaural.