After you left, I spent some time making a few small adjustments to the speaker position, listening position and diffuser locations.
I was floored by what I heard with the rack in situ.
EVERYTHING sounds better.

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The top end is cleaner and more resolved. Bass and dynamics improved substantially. A lot of the unevenness and boom I was hearing previously has disappeared. Low frequencies are D-E-E-P, tight, punchy and texturally nuanced.

 

The differences are obvious and to say I'm impressed with the sound quality improvements would be an understatement. I was so enamoured by what I was hearing that I went on a musical deep dive and didn't end up leaving the office until 6.30pm!