A. Modern producers, when they need reliable sources of original equipments and technologically advanced components to operate profitably, face increasingly difficult choices of owning the producers of these items, a practice known as backward integration and buying from independent manufacturers
miss comma btw modifier "a practice known...integration" and part of parallelism "and buying from". Also when should modify a time or adverbial modifier, but modern producers is not an adverbial modifier such as "by Monday"
B. Modern producers, who need reliable sources of original equipments and technologically advanced components to operate profitably, face an increasingly difficult choice between owning the producers of these items, a practice known as backward integration, and buying from independent manufacturers
who correctly modify subject "modern producers"; idiom between x, and y is correct, note here the modifier is too long that a comma to break the two parallel items is necessary; also parallel structure is perfect "owning X-ing, modifier, and Y-ing"
C. Modern producers, who need reliable sources of original equipments and technologically advanced components to operate profitably, face an increasingly difficult choice to either own the producers of these items, and to buy from independent manufacturers, a practice known as backward integration
wrong idiom and structure either X or Y not either X and Y. Also wrong to have "either own, and TO buy"
D. Needing reliable sources of original equipment supplies, and technologically advanced components to operate profitably, modern producers facing an increasingly difficult choice of owning the producers of these items, and buying from independent manufacturers, a practice known as backward integration
This is plain wordy and awkward.....
E. Modern producers practice what is known as backward integration, when they need reliable sources of original equipment supplies and technologically advanced components to operate profitably, and to face an increasing and difficult choice of owning between the producers of these items and buying from independent manufacturers
too many things wrong: i.e. not parallel "Sub practice......, and TO FACE.."; second and structure also wrong