Video : AVC @ ~24595 kbps
Audio : DTS-HD MA 5.1 @ ~3938 kbps
Audio Commentary: DD 2.0 @ ~224 kbps (Episodes 2 and 24)
Chapters : Yes (Not named)

Source : The.X-Files.S01.1080p.Blu-ray.AVC.DTS-HD.MA.5.1-jimsong (Thanks!)