+ 6 new skills (walker same as NeoLemmix, others different)
Platformer too. It does function slightly differently, but it's essentially the same skill.

I have the NeoLemmix level editor, but it seems really complicated.
Are you using Lemmix Editor or jLevelBuilder for your levels? If you're using the former, the NeoLemmix Editor isn't too much different (and even if you choose to stick with SuperLemmini, the NeoLemmix Editor will allow you to use some SuperLemmini features that didn't exist in regular Lemmini and therefore aren't supported by Lemmix Editor / jLevelBuilder).
And indeed, NeoLemmix does support WAV music, though as mentioned above it isn't recommended.
In my opinion at least, the only real advantages SuperLemmini has over NeoLemmix are higher-resolution graphics, and cross-platform support (although this is to some extent negated by the fact that NeoLemmix works fairly well under WINE on Mac / Linux). Lix has neither of these disadvantages, although it does lack music support, and may not feel as "Lemmings-y" due to it using only newly-made graphics. Do be aware that while it's quite easy to port content from SuperLemmini to NeoLemmix (and in reverse, provided you don't use any NeoLemmix-exclusive features), it's much harder to port between those two and Lix.