If you are interested in the intersection between Buddhist and Western philosophy, a good place to begin is with Mark Siderits's book, Buddhism As Philosophy: An Introduction. Tom McEvilley's book The Shape of Ancient Thought offers a historical perspective of the inter-connections between the ancient Greek and Indian philosophical traditions.
Now, as to your more specific question: the canonical source on this matter is SN25.23, the Sabba Sutta, where "the all" is defined as: "Simply the eye & forms, ear & sounds, nose & aromas, tongue & flavors, body & tactile sensations, intellect & ideas."
As you no doubt know, the Kantian distinction between the sensible and the intelligible is, in Buddhist thought, collapsed into one level, so that they speak of six senses: the five traditional senses plus the "mind" or "intellect"-- and each of the six has a "sense door" (the eye, the ear, etc.) plus a field or domain of sense (vision, sound, etc.)
So, "the all" is defined as the six senses plus the domains of each of the senses.
Put another way: "the all" anything that is capable of being experienced in any manner whatsoever.
As the Sabba Sutta explains, claiming knowledge of something outside of "the all" would be self-defeating: "if questioned on what exactly might be the grounds for his statement, [her] would be unable to explain, and furthermore, would be put to grief. Why? Because it lies beyond range."
Is it for example both a rational and empirical way of seeing the world, is it one among other similar perspectives, is it defensible?
It superficially appears to be empirical, but is somewhat different than empiricism as traditional constituted, because of the inclusion of the intelligible. It is an eminently defensible position; I don't know off-hand of any philosophers who dispute it (although there may be some I am not remembering at the moment.)