Arts/ESD(Esound)/etc are sound servers, or mixers rather... applications pass sound to these programs instead of directly to the sound device.
This allows neat effects like hearing your songs while also hearing audible alerts from instant messaging clients etc.
Sun typically refers to the interface used by the /dev/{audio,sound} devices, often that means it'll directly manipulate the sound devices or use
ossaudio(3), an OSS-compatibility layer.. you should note, this will temporarily prevent other applications from playing sound.
http://en.wikipedia.org/wiki/Soundserver
http://en.wikipedia.org/wiki/ARts
http://en.wikipedia.org/wiki/Enlightened_Sound_Daemon
http://en.wikipedia.org/wiki/Open_Sound_System
http://www.openbsd.org/cgi-bin/man.c...nt&format=html
Have fun..