Booting without a startup-sequence has the audio, if you've booted with user-startup once. At least here with Delfina Lite.
About DSP use.. I think there was some effects thing in drivers package, can't remember or check just now, but for me the most important thing is the mpeg-decoding. You can decode mp3 audio with Amplifier, AmigaAmp, DelfMpeg etc and Frogger can use audio hw decoding with videos too.
