I have a gmplay-2.0, which plays video in one thread and "noisy rhythms" audio in another thread. On my k5, it plays perfectly, using abou 12% CPU. Of course, knowing that the K3 eink update burns CPU, I need to test it there too... EDIT: On the K3, it burns 93% CPU (mostly in the eink update call). But the video plays full speed even with synthesized sound. EDIT2: After recompiling with optimization (-O3) it now uses 82% CPU on the K3 -- a useful improvement.
UPDATE: My K3 sound works (for noisy and tones) after turning down the volume. It must have some kind of overload detection that makes it drop out for a bit if it is too loud. I had it turned up for the quiet 8kb8mono.wav|aplay test (which is still quite even at max volume).
So, if there are sound dropouts, turn down the volume.
The next step in this path of combined Audio/Video evolution of gmplay is to use sound interleaved into the video file, instead of synthesizing it.