I don't really get what you're trying to say but these cards for the Amiga are soundcards that have a on board DSP. This processor can be used to decode MP3 in hardware. At least that's what the Delfina is. The DSP can also be used for other things (adding soundeffects for example) but I don't use that. The card is used from Workbench so it's not like a seperate MP3 player.
Next to that the Delfina is also a 16bit soundcard that features a mixer to mix audio sources (native Paula Amiga sound, Delfina sound and CD-ROM sound and in my case Picasso TV tuner sound).