OK, the first step is to ensure MC6 recognizes the Akai.
Ideally, your keyboard should be connected to the computer before you open MC6.
Start MC6, and create a New project, using a blank template with no tracks.
In the tool bar, click Edit>Preferences>MIDI Devices.
In the Inputs box you should see UX2 MIDI IN and the Akai listed.
Depending on its drivers, the Akai may be listed by name, or it may show up as USB Audio Device.
Place a checkmark in the box next to the Akai.
Do Not select any MIDI outputs. You don't need them at the moment.
Click Apply, then OK to close the preferences window.
At the lower right hand corner of your screen, you should see an icon that looks like a tiny keyboard.
Hit some keys, and the red light on the left side of the icon should flash. This tells us that MC6 is receiving MIDI from the keyboard.
So far, so good?
Now, insert Studio Instruments Drums, selecting the options Greg shows above. Also select Synth Properties Page. This will open the synth GUI.
SI Drums opens with a default kit, but for fun, click the PRG(program) box, and select Room Kit.prog from the drop-down menu.
Input echo should be turned on in the MIDI track.
Hit some keys. Do you hear drums?
If not, the keyboard may be in the wrong octave range. This is a very small keyboard, and the drums are in the lower octaves. Shift the octave down if you need to.
At this point, you should be hearing drums.
You would insert EZDrummer the same way, but I chose SI Drums because it is simpler to use.