The need of a fs-scale pulsed, MHz-class repetition rate, X-ray source for time-resolved fine analysis of matter (spectroscopy and photon scattering) in the linear response regime is addressed by the conceptual design of a facility called MariX, outperforming current X-ray sources based on FELs or Synchrotrons for the declared scope. MariX is based on the original design of a two-pass two-way superconducting linear electron accelerator, equipped with an arc compressor, to be operated in CW mode with up to 1MHz repetition rate. MariX provides FEL emission in the range 0.2-8 keV with up to 10^10 photons per pulse and up to 10^16 photons/s using a 1.5 GeV Linac, but delivering to the FEL undulators up to 3.8 GeV electrons. The accelerator complex includes an early stage that supports an advanced inverse Compton source of very high-flux hard X-rays (up to 10^13 monochromatic X-ray photon beams), of energies up to 180 keV, that are well adapted for large area advanced radiological imaging. Such a complex enables a broad science program and will serve a multidisciplinary user community, covering fundamental science of matter and application to life sciences, including health at preclinical and clinical level. MariX C.D.R. has been recently published on its dedicated web site: www.marix.eu.