Im not sure, but i think delfina (and other cards too) does not have any MP3 DPS decoder, so you can play it 16bit/stereo , but load will be same as without any card.
IF you need to play MP3 with small cpu utilisation, try to lood for MAS MP3 player on paralel port. With 130/50 you will be able to play almost all MP rates without noticing it
