For whatever reason I can't play any audio stream at hummaa.com.

They use flash player. HTTP streams from flash player can be easily recorded. You can download them even with your browser.

As for RTMP streams, you can try Replay Media Catcher and FLV Recorder. Please note that, unlike Replay Media Catcher, FLV Recorder can record FLV streams only.

And I don't know how to find RTMP stream URL for Orbit Downloader.