What exactly is textural density??

Herein lies the difficulty in describing how our brains process sensory stimuli

No two people interpret this exactly the same.

As a musician in an orchestra with 44 other instruments, we spend a lot of time working together to create a rich, multi-layered harmonic sensory experience. Some might call that 'textual density'. Others, simply 'music'. 

String players work together and focus on playing certain notes using specific bowing techniques. When they all get it right, it is magical.

As a brass player, the goal is to always be 'centered' on the note (this is the same concept that opera singers focus on). That is when the richness of the instrument's tone comes alive. 

I try to mimic that sensory experience in my system. Can I discern (hear) the instruments' under tones, harmonics, and partial harmonics? The decay of individual notes? Each section's contribution to the overall sensory landscape?

My goal is to be able to close my eyes while listening to a recording and feel like the musicians are in the room with me.

I happen to have a PHD in Textual Density. My dissertation was on the Rosetta Stone. 

I happen to have a PHD in Textual Density. My dissertation was on the Rosetta Stone.

I just begin to read your dissertation.... Congratulations!

https://www.amazon.com/Timbre-Acoustics-Perception-Cognition-Springer-ebook/dp/B07RMT74YN

Another great catch by Mr Magister!  That link is a great portal into the science behind all this audio psychology.
Music is the MOST abstract of all art forms. The result, when trying to describe abstract ideas, is usually metaphor.  Try writing down how it felt to get your last orgasm AND WHY and you’ll approximate the dilemma faced by any published critic.

Textural density to me means palpable,  having body, 3 dimensionality. I get this “feel” in the lower frequencies as heft, weighty slam .   In the midrange as layering , having mass.  Not so obvious in upper frequencies but discernible as having mass even if the sounds float between speakers.  One way of experiencing this is to compare different systems.  Once you pick it you will understand it’s meaning