I'm increasingly inclined to turn to Luangta Maha Boowa's words for clarification on all this.
from Samana – Luangta Maha Boowa Memorial Book p. 91http://www.forestdhammabooks.com/index.php?page=Books
"At the beginning of our practice the heart
had no worth, since it was filled with nothing
but the excrement of greed, hatred and delusion.
By totally washing away that excrement using
the principles of the Dhamma, the heart itself
becomes pure Dhamma. Once that happens,
it’s infinitely at ease. Wherever you go, you’re
at ease. “Nibbana is the ultimate void.” Whatever
is annihilated in that void, this you’ll know. Whatever remains there, this
also you’ll know. Who can know this better than one without defilements? The
Buddha, in saying that Nibbana is the ultimate void, was speaking from his
absolute freedom from defilement. He said this from having seen Nibbana. But
we haven’t seen it yet. No matter how much we repeat his words, we just stay
where we are. Investigate so that you truly see it. The saying “Nibbana is the
ultimate void” will no longer be a problem, because what is annihilated and
what’s not will be fully clear to the heart.
“Nibbana is the ultimate happiness.” Listen! The ultimate happiness here
isn’t a feeling of pleasure or happiness. Instead, it’s the happiness that comes
with the absolute purity of the heart, with no arising or ceasing like our feelings
of pleasure and pain. This has nothing to do with the three characteristics
of existence. The ultimate happiness as a constant feature of the pure heart has
absolutely nothing to do with the three characteristics, nothing at all to do with
impermanence, dissatisfaction and not-self – it doesn’t change, it always stays
just as it is.
The Buddha says Nibbana is constant. What’s constant? The pure heart
and nothing else; that’s what’s constant. Get so that you see it, get so that you
"When one thing is practiced & pursued, ignorance is abandoned, clear knowing arises, the conceit 'I am' is abandoned, latent tendencies are uprooted, fetters are abandoned. Which one thing? Mindfulness immersed in the body." -AN 1.230