Now that this setup seems to be stable and working well, I went back to testing some frequency generator apps on my Android HTC Incredible. (I've got a hankerin' for a somewhat more portable setup.)
I've got four of them installed and the one that produced the best results (which was also very close in intensity to my laptop and Multisine V1.74 combination) was the Frequency Sound Generator app. The interface is very user-friendly and it has never acted flaky. I tested it with a square wave at 10hz in loop mode. Nice! (Your mileage may vary.)