Well the X-Fi IS your audio interface, atm
(not that I really recommend using that kind of card for producing, but still). Really don't use LINE level signal on a MIC input unless the manual explicitly tells you to, though. You'll also be limited to only 2 mono channels at once / 1 stereo channel - you won't be able to simultaneously process more than 2 sounds with different FX, since the card doesn't have any more inputs and can't manage more.
Also, you don't really need a 2+2 MIDI interface unless your keyboard controller doesn't have a USB/MIDI interface (which is a bit weird unless you're using an old one or a prosumer rompler-like keyboard; in the latest years it's been quite the opposite, i.e. entry level controllers don't have a physical MIDI port any more, like KeyRigs and QSs). Which keyboard do you have? There's even a couple of the that can act as a MIDI interface for what it's worth (old M-Audio Keystation comes to my mind).
Last thing, I usually say it like the MIDI interface and sound card are two separate entities because some sound cards have no way to implement a MIDI interface. Many others do, though, and those do not require an additional MIDI card