Okay…things I am quite familiar with.
MIDI: if you are trying to connect the MicroKorg so that it can be used as a MIDI controller and/or have the software trigger MIDI, you’ll need a MIDI Interface.
Some Interfaces out there combine MIDI and Audio; otherwise, you can get a dedicated MIDI interface to do the job (This would be a MIDI to USB dongle or box, that has both MIDI In and MIDI Out).
As for your Audio Interface, that device will only allow you to get the audio output of the MicroKorg into the computer so that it can be recorded into your software. Key to this is making sure your Audio Interface:
1.) Is stereo-capable-that is, it has two physical inputs. If one input is XLR, the other ¼”, the key is to find out if they both accept line input, and if they are in fact two separate inputs. In some cases, two ports does not necessarily equate to two inputs. On the device, the inputs should be numbered, so if your Audio Interface’s two jacks are labeled “1” and “2” that would indicate two physical input paths to the computer; and
2.) Your Audio Interface requires drivers to connect it to the audio software and your system. For Mac OS X, in most cases, the drivers are pre-installed with the OS; however, in some more obscure manufacturers, the driver is not pre-installed, and you will have to download and install the driver, from the manufacturer’s website. In any case, their website will tell you if the AI is “plug and play”
Now if both of those conditions are satisfied (your device has two input paths, and you have the proper drivers installed), then you should be good to go, even if the jacks are two different types, you can remedy this with a simple converter jack (XLR male – to -¼ female adapter). Then you would take your stereo ¼” cable and connect from your Korg’s stereo output to the AI’s two inputs, then in the DAW app you’re using set up the audio input in the System Preferences of the App, or in Apple/System Preferences/Sound Input tab.
If the above is a no-go, there are affordable solutions that give you both stereo audio input/output, and MIDI I/O; a reputable solution is to go with M-Audio, and one interface I can vouch for is their FastTrack Pro. It has 4 audio inputs (including 2 XLR mic inputs with phantom power for powering condenser mics), 4 outputs, 2 audio inserts, and MIDI I/O. The link is here: http://www.m-audio.com/products/en_us/FastTrackPro.html
You can find that interface on eBay or CL for around $125 fyi…and it’s well supported as M-Audio updates drivers constantly, and they’re a subsidiary of Digidesign (makers of ProTools).