I had successfully imported my HLS sequences over to xlights around 3 or 4 years ago, back when version 4 came out. I believe Dan developed the import for HLS since he was a HLS user before becoming an xlights developer.
I'll admit, it was a while ago but I believe the steps I followed were:
1. Setup the Lighting network exactly as I had them when I exported my HLS files (HLSdata files). in other words I setup all my controllers and universes exactly as I had them in HLS.
2. Created all my display elements in layout of Xlights and named them as I had in HLS.
3. Once all that is setup, you can create a new sequence and select your music.
4. Select import and then import effects and point to the HLSDATA file you exported from HLS.
5. You have to select the models you want to have the effects import on and then you can select the HLS nodes to import.
Now this part can be tedious, but you only have to do it once and then save the mappings. Once done, you can import the next sequence and use the same mappings.
As stated before, once imported you can't really edit things since it is a flat data layer import. However, for those few HLS sequences I still use I just add to it in HLS and then re-export and re-import to Xlights. This is a labour of love for those few sequences I have lot of time put in like yourself. Newer sequences are made with xlights only of course.