Hi Philip,
Sorry you're experiencing this trouble. The good news is it looks like we can clear it up quickly.
I switched my board's self-boot switch to enable and duplicated your symptoms exactly -- it runs for one second, makes some loud "burp" noises and quits. Actually the self-boot should be disabled when running from SigmaStudio using the USBi. Only enable it when actually testing the chip's self-boot feature. With the USBi and SigmaStudio connected, the chip boots directly from SigmaStudio via the USBi -- in this case, self-boot gets in the way.
When you wish to test self-boot, first load the on-board EEPROM with your compiled project, then disconnect the USBi and power up or reset the board (with self-boot enabled now) to self-boot. See page 17 of the user's manual. On-screen controls don't work in this mode (whether the USBi is connected or not). In an actual self-boot system, your custom board would have pots or buttons connected to the chip's MP pins to control user functions.
I tried headphones on my -1452 board, it drives them OK at low volume. Amplified "computer" speakers work really well.
Hope you'll be "on the air" really soon!
Bob