Thank you for the help, even though it does not make me to advance.
I'm not mission analyst, but I know a bit of Orbital Mechanics. Its just that I have an xyzv file (representing a drifting elliptic orbit), that was produced by a mission analysis tool, but the outcomes in Celestia looks not the same. The reference frame in which those were computed is an Inertial Reference Frame centered on the Planet.
In the ssc file I used the "EquatorJ2000" reference frame and said to use the positions in the xyzv file.
In the outcomes it looks as the inclination is correct, therefore an equatorial frame is correct, but that the apoaxis is not where it should be. I suppose therefore a problem in the apsides line of the reference frame, as the X axis of the reference frame would not be the correct one. For such a reason I asked previousely if the EquatorJ2000 and EclipticJ2000 are not simply referenced to the Earth. They could be applicable to every planet, but keeping in mind that the X axis is always oriented toward the Aries point, which is, obviously, valid only for Earth.
I may check in using the MeanEquator at the date in order to see if this solves the issue.