Among the fathers of the ancient church, I always thought that the concept of salvation was best
expressed in the works of Cassian. Was Cassian semi-pelagian? I would say no. Besides, the charge of semi-pelagianism is one often brought against the Eastern Orthodox view of salvation generally, though I doubt many Orthodox would consider their view heretical. I'm sure there are statements in the works of Cassian that wouldn't be acceptable to everyone, as everyone makes mistakes.
I am obviously not saying that I agree with him about salvation, I just think that Cassian takes the various statements and contradictions (free will vs. determinism and such) in the bible and synthesises them pretty well, not falling into extremes. I guess one of the things that might catch someone's eye in Book 13 is something like this...
"For we should not hold that God made man such that he can never will or be capable of what is good: or else He has not granted him a free will, if He has suffered him only to will or be capable of evil, but neither to will or be capable of what is good of himself." - John Cassian, Conferences 13, 12
However, there are also ideas like the following in the works of Cassian...
"'For it is God which worketh in you both to will and to do according to good will.' (Phil 2:13) What could well be clearer than the assertion that both our good will and the completion of our work are fully wrought in us by the Lord?" - John Cassian, Conferences, 3, 15
Half this 3rd Conference discusses free will in this way, emphasising the part that God plays and minimizing the part that humans play (esp. Chapters 11-22
Here are some other quotes from his works...
"...the initiative not only of our actions but also of good thoughts comes from God, who inspires us with a good will to begin with, and supplies us with the opportunity of carrying out what we rightly desire: for 'every good gift and every perfect gift cometh down from above, from the Father of lights,' (James 1:17) who both begins what is good, and continues it and completes it in us, as the Apostle says: 'But He who giveth seed to the sower will both provide bread to eat and will multiply your seed and make the fruits of your righteousness to increase.' (2 Cor. 9:10)" - John Cassian, Conferences, 13, 3
"Whence human reason cannot easily decide how the Lord ...draws men against their will to salvation, takes away from those who want to sin the faculty of carrying out their desire, in His goodness stands in the way of those who are rushing into wickedness." - John Cassian, Conferences, 13, 9
(There are a lot of other parts in the 13th Conference
that are closer to Augustinianism than Pelagianism). But one last quote, from the Institutes...
"For the will and course of no one, however eager and anxious, is sufficiently ready for him, while still enclosed in the flesh which warreth against the spirit, to reach so great a prize of perfection, and the palm of uprightness and purity, unless he is protected by the divine compassion, so that he is privileged to attain to that which he greatly desires and to which he runs. For 'every good gift and every perfect gift is from above, and cometh down from the Father of lights.' (James 1:17) 'For what hast thou which thou didst not receive? But if thou hast received it, why dost thou glory as if thou hadst not received it?' (1 Cor. 4:7)" - John Cassian, Institutes 12, 10
Can't really help you much regarding the Council of Orange or Augustine, leastwise I can't help any more than going and doing a Google search and posting the findings here (which you could do yourself, you don't need a wicked apostate for that