@kylix, I can show you what I managed to cobble together from lots of other examples. I'm using the MAX8914 in two ways, 1) As a simple measure of sound level, and 2) To record sound onto the SD card. I've been back and forth between the SD and SdFat libraries, and have currently settled on SD. I know SdFat is supposedly smaller and definitely offers more options, but for what I'm doing SD is currently meeting the needs. There were the usual challenges of getting an SD card reader to work on the Mega with the radio, and sometimes it requires a hard reboot when loading new code and the SD card fails to initialize.
From the menu I can choose to display the sound level, start/stop recording, perform a file directory (limited to WAV files), and delete files. I toyed around with adding a format option but punted that one. I initially wanted to be able to transfer the WAV files over the RF radio but gave that up after figuring the drain on the batteries of transferring multi-megabyte files. For now, when the rover "goes home", I will simply remove the SD card. I'm using Audacity to experiment with cleaning up the sound quality, which is actually pretty good for a cheap microphone. I also added a "card not present" function that is checked to make sure there is an SD installed before every write.
I didn't play around much with the gain and AR, since my rover is being designed to live outside 24/7 and I figured I wanted to get as much sound captured as possible.
You'll get to see more when I post the code.