Comparisons

Microkorg MK1 VS. Microkorg XL

The XL is much better than the mk1. It has twice the polyphony, the vocoder is much better, microphone and keyboard are better. The Microkorg XL is based on the MMT engine which powers the Radias.
 It's a newer engine than what powers the original MK and is more powerful in general and capable of a wider range of sounds. The display on the XL keyboard themselves are much more helpful than on the original MK.