In one sutta in the Digha Nikaya (I am forgetting which one), the Buddha says that in a previous life, he discovered the way to rebirth in the Brahma realm, i.e. 4 Brahmaviharas. However, this did not lead to the ultimate goal of Nibbana. In contrast, in his current lifetime, he discovered the Noble Eightfold Path, which led beyond all realms, including the Brahma realm, to the ultimate goal of Nibbana.
Thus, the latter (the Noble Eightfold Path) was contrasted with and given primacy over the former (the Brahmaviharas).
That being said, both seem to be integral and fundamental parts of the Dhamma-Vinaya.
My initial thought is that it might be more helpful to think of all the various factors mentions within the Dhamma-Vinaya as distinct and independent factors, and not assuming relationships between them unless a relationship between the factors are explicitly stated by the Buddha.
For example, I have not come across any discourse where sila is considered an engine for the N8FP, but I have come across a discourse where right view could be seen as an engine of sorts that leads to arising of the rest of the seven factors of the N8FP:
Bhikkhus, just as the dawn is the forerunner and first indication of the rising of the sun, so is right view the forerunner and first indication of wholesome states.
For one of right view, bhikkhus, right intention springs up.
For one of right intention, right speech springs up.
For one of right speech, right action springs up.
For one of right action, right livelihood springs up.
For one of right livelihood, right effort springs up.
For one of right effort, right mindfulness springs up.
For one of right mindfulness, right concentration springs up.
For one of right concentration, right knowledge springs up.
For one of right knowledge, right deliverance springs up.
Anguttara Nikaya 10:121
Thus, unless relationships between factors are explicitly stated as described above, I think it might help to treat all the factors of the Dhamma-Vinaya as independent and distinct - each seems to merit a suitable degree to attention to be developed to a sufficient degree necessary for the attainment of Nibbana.
Another relationship that can be assumed is that unless all eight factors of the N8FP are included, a course of practice is not sufficient for the attainment of Nibbana - for example, the 4 factors of the Brahmavihara (with or without sila) are not sufficient for the attainment of Nibbana.
Another relationship that I am slightly less sure of than the one I just previously claimed is that all the concepts within the Dhamma-Vinaya as a whole can be contained within the Four Noble Truths and all the practices within the Dhamma-Vinaya as a whole can be contained within the Noble Eightfold Path - or something along these lines.
I find that thinking in terms of the Sila or Brahmaviharas alone to be less sufficient and complete than say the Noble Eightfold Path (“bare minimum” factors necessary to attain Nibbana) or the Dhamma-Vinaya as a whole (“complete” version of what the Buddha taught and trained as being the “full scope” of what is “relevant for” and “conducive to” the attainment of Nibbana).
I hope that this way of thinking helps.