Forgive me, Michel. I am about to throw a wrench in this.
As I understand your most recent post, in my limited experience, the brahma-viharas act as a door to samadhi 5-8. For example, the most profound jhana experiences I've had were preceded by an hour, day, month or longer of being in one of the brahma-viharas. With established brahma-vihara, I would then enter jhana and be thrust by incredible energy/ecstasy beyond 4th jhana and into a state I cannot describe other than "Home", "God" or "It." This explains on the GWV jhana page why the samadhi's are called "god of infinite consciousness. When I come back from these, I feel a strong sense of enlightenment. I think this accounts for the Buddha's use of "liberation of mind."
Now I used to think that beyond 4th jhana was simply the 4 samadhi's. But this has not been true in my experience. When I enter jhana without being established in a brahma-vihara, I experience jhana of a lesser profundity. If I then go beyond 4th jhana, I experience devas, "astral" travel, other worlds, remote viewing, and other OOB phenomena. I've come to feel that this is the stage in-between 4th jhana and 5th samadhi.
In other words, it seems the 4 samadhi's, referred here as base of infinite consciousness, or base of nothingness, etc, are only accessible through entering meditation from a mind that is presently and strongly established in a brahma-vihara. Otherwise the deepest one can usually get is OOB phenomena.
Beyond 4th Jhana from Strong Brahma-Vihara = High Chance of Entering Samdhi 5-8
Beyond 4th Jhana from an ordinary human mindstate = OOBE Phenomena
Lastly, I want to mention that before I became firmly established in daily jhana, I experienced over a year of meditation practice where I was blissed out in ordinary daily life on nothing more than a mind cultivated in brahma-vihara (which of course requires mindfulness.)
Both intellectually and intuitively it seems that this information is accurate. But it is the first time I've realized this, thanks to your coincidental mention of this subject. I spent a lot of time in 4th jhana on this topic today.