There are several possible reasons for the 'tarriel cell compatible technology' of Zen/the Liberator/the System (Orac has 'no apparent problem' in overriding System computers).

a) Independent but parallel development sufficient for Orac to understand. Going by 20th/21st century computers this is 'unlikely.'

This implies some communication between the System and the Federation - probably one way as even Servalan/the Federation High Command are unaware of the System. (This would also imply that the System is 'not in the direction of' Andromeda/Horizon, or the Federaiton would have come into contact with it.) Correlating the information in 'Orac' and 'Redemption' the System's space centre was probably constructed long before Ensor developed the Tarriel cells.

b) The System goes technology hunting (the equivalent of the Chengas?) - the Liberator/DSV2 is one of a series of such ships, but went close to the battlefield to acquire 'equipment' and got caught in the crossfire.

c) My previous suggestion that Ensor came from the System, bringing the tarriel cell technology to the Federation. (This might explain why he did not have his mechanical heart replaced - incompatible tissue types.)

d) Ensor (who, it appears withdrew from the Federation so he could get on with his researches privately) encountered an earlier System spaceship with 'tarriel cell equivalent technology' and made use of its technology. Neither this nor c) reflects against Ensor's capacities in making the two systems compatible.

Any other possibilities?

As for Avon - when would he have come from the System (and why?)

There is no evidence that he came from anywhere other than Earth/the Solar System (Gan might, as he habitually wears a different costume to the others - the equivalent of 'regional dressing' now). If he had 'suddenly appeared' a few years before, he is unlikely to have been given access to some of the things he was - the banking system and the teleportation project.

If he was a former inhabitant of the system he probably moved as a child (which, if he was 'mechanically gifted' would still enable him to have some idea of the technology he left behind).

He could also have a strong visual memory - and there is a #very# noticable constellation in the bit of the System's sky we are shown.

It would be ironic if Avon came from a family which left the System because they disagreed with it, and got caught up in an attempt to overthrow the Federation.

Jacqui