Eh, Mad provides useful information a lot of the time... I was thinking the same thing when I read this post originally because MIDI got thrown around so much, it confused me what you were tryin to do.
Anyhow!
Midi is not a digital or analog representation of a musical instrument's AUDIO signal. It is simply a protocol for sending data. More specifically, let's take a synth or electric piano that has midi Input/Output, and you have an interface that has (in part) midi I/O.
Once you plug the cables in to attach the two, you set up your recording/sampling/recording/whatever software to send/receive midi information. This information is, once you start playing the piano/keyboard, data that describes what keys you are hitting, how hard you hit them, any information about what pedals you have pressed down, and what knobs on the keyboard are set to.
The software that is sync'd to this midi I/O then takes that data, and plays sounds according to what keys you are pressing, etc etc (or records this data for future playback, depending on what you want to do). However, the keyboard itself in this situation is NOT making any sound. The keyboard and midi interface to the computer are equatable to, say, setting up the keys on your computer keyboard to make different sounds when each key is pressed, respectively, and that's it. The method of receiving the data is different, but the concept is the same.
If you are confused about any of this, feel free to ask. I was very confused about how data was transferred via midi connections when I first got into all this myself, so I know your pain (and people here can be rather unforgiving on occassion, if you don't word questions properly).
As for recording live sounds (guitar amps, drums, etc), you will need to either get a multi-input interface such as the firepod, mentioned above, or a mixer. The benefits and drawbacks are different between the two.
If you buy a Firepod, you can, as described above, record 8 individual mics worth of audio into 8 separate tracks on your computer, and manipulate them individually before mixing them all together. This is the most flexible recording means, but you would have to buy a Firepod.
On the other hand, you can buy a mixer that takes as many mics as you have/need, but you would then have to run the stereo output of your mixer to the Emu, so you would need to have the mixer's settings as you want them before hitting record. Once you are done recording, you can't do things like increase/decrease the volume of an individual instrument/vocal. The plus? You didn't have to buy the Firepod. However, if you are already buying a mixer, why not go for the most flexibility?
I didn't think of it before, but there is a third option... Alesis and some other companies make mixers that have firewire output that you attach to the computer, and (I believe), this allows you to record each channel of the physical mixer in your multitrack recording software, on separate channels. You'd have to hunt around for info on that though, as I've never used one before.
Sorry for the rant, but I got rather into the explanations... and Im bored at work before meetings, so long explanations are a nice way to pass the time - if you already knew any of this, sorry for the extra reading! Im off - feel free to ask questions when searching yields little or no results
