I have no experience of using any Amiga soundcards but I have looked into the options available. Most of them are 16-bit AD convertors and codecs (in these I would class the Tocatta, Prelude and maybe Repulse). The ones that are more exciting to me are the Delfinas which have come in a number of flavours over the years. These cards have an onboard Motorola 56k DSP which can be used for FX or MP3 decoding without straining the Amiga CPU. I get the impression though that any Amiga soundcard is a bit flaky and this is what has stayed my hand from reaching for my wallet. The only soundcard currently available new I think is the Delfina Flipper (see Amigakit). ;-)
