What exactly is textural density??

If you are a hi-fi magazine writer, you are largely describing sound.
This is certainly not easy and you need real talent, nay imagination, to invent hundreds of expressions to do that.  Otherwise every month's copy would be much the same.
It appears that the creators of the most flowery, ambiguous and vaccuous expressions are the most successful hi-fi writers.
My advice, Erik: read John Atkinson, not Herb Reichert, as I have done for more than 40 years.

It’s perhaps described as a combination of textural density tone and weight IMHO. A note has a beginning middle and end and it is the ability to fulfill these

@erik_squires 
Anything in music that doesn’t sound like an AM radio. And then like anything else there are different degrees. 
Hope that helps!

John Atkinson's writing may be clearer, but his conclusions are inscrutable.

+1 to cheeg!
We've all used adjectives like "threadbare", "thin", or the old standby, "tinny" to describe sound reproduction that reduces the "richness", "color" or "warmth" of the music.  This is just another positive adjectival phrase in the same vein.  All this for those of us with BA degrees not EEs.