The Xtreme Music will be better than the A2ZS for music. But it is still more of a gaming card: I seem to remember that the Xtreme Music -> Fatal1ty range of card all use the same DAC/Op-amp as the A2ZS (or if different not much upgraded - only the Elite Pro is different). BUT they are still better for music because it doesn't resample (in Audio Creation mode), and have a better resampling algorithm compared to the A2ZS (in other modes).
The EMU 0404 will be a (not major from some sources - I don't have first hand experience with those) step up to the X-Fi series minus the Elite Pro (you are starting to venture into audiophile terrirory). The EMU 1212 is very similar to the Elite Pro, but without the latest gaming features (at almost half the price of the Elite Pro too). In truth the X-Fi also uses EMU chips, but they don't use the same op-amp/DAC as the actual EMU cards.
For simplicity, it is probably better to go X-Fi though. You'll have more people able to troubleshoot around here, and you are not going to use some mid-high end headphones right?