MIDI Designer is plug-and-play with all CoreMIDI compatible hardware for iPad. It’s been tested with the Line6 MIDI Mobilizer II, the Apple iPad Connection Kit, the iConnect MIDI, and the iRig MIDI
The most direct option is to use iConnect MIDI, which will allow you to directly connect to your computer and other iPads.
To connect with the Line6 or the iPad Connection kit to your computer, however, you’ll need an additional piece of hardware. For the Line6 MIDI Mobilizer II, in addition to the device you’ll need a simple USB MIDI hub for your computer. Note that the Line6 has male MIDI cables out, so you’ll need female ports into your computer (or gender changers). One example of such a hub is the MIDIMAN MIDISPORT 1x1 Multiplatform USB MIDI Interface. Another is the Edirol UM2-EX.
If you have or can get the hardware, this works perfectly. If not, consider using an Ad-Hoc (Computer-to-Computer) connection for lower latency, greater security, stability, and no additional cost.