i dont see why we have to make everything so difficult.
to first address the thread starters post
what is the profound question here exactly?
the universe is a large mass, a large mass made up of strings, or particles or whatever it might be. however what it is made up of is irrelevant.
you can do many things with these particles. (lets just say the universes smallest parts are particles for the sake of argument).
they bind and push eachother away and you get things like a sofa, a computer, a human.
now, a human has the power of observation. we can SEE the world. we are sentient.
so you asked about the sofa.
either the sofa can be a figment of someones imagination, like in the matrix.
if it is, its a neuron state. an electrical impulse in the brain, a vague semi metaphysical sofa.
if the sofa exists in the real world its made up of particles, and other particles can interact with it.
so whats the problem with existence?
just say "its all a big blob of particles, some things exist on a metaphysical level, in an observers mind, and other things exist as physical particles."
and then boulderhead. if we proceed with the particle theory.
every particles that is in the universe /exists/. the meaning of the word exist means /to be/ to be /something/.
"nothing" is then all those things that DONT exist. the particles do not exist.
the only way we can put a form or explain nothing is to say that it is the absence of /something/. but literally nothing is all that does not exist.