I'm pretty sure X-Trans I and II will work with LR 5.6. I recently procured the X-Pro2 and had to move up to LR 6, which supports both uncompressed and lossless compressed.
In summary, LR will work fine with X-Trans files, but I was never that happy with the way LR rendered them. The LR Classic Chrome profile was not close at all to Fuji's, and I just didn't like the way the files looked very much. Thomas Fitzgerald's sharpening presets were very handy, but on balance I think Capture One Pro 9 does a much better job than LR.