There is also one other factor George, placement of Front L/R vs. center. Most often the Front L/R are closer to corners/walls and that could attract some "boominess" from vented enclosures, more so than their sealed friends (DSP8k/DSP6k) IMHO.

I have noted your past description of DSP5.5kHC being less boomy than DSP5.5k before but I have not made that observation yet.

DSP8000SE, DSP7200SEHC, DSP5200SE sides, DSP7200SE rears, 861v8, 210, Sim2 Ultranero 4, Stewart Cinecurve 2.35:1, XEIT CM-5E Anamorphic lens, Dune HD Duo Cinema 8K and Wireworld Platinum 48G HDMI -> UHD722 -> Shunyata Omega Ethernet. Shunyata/Furutech power-cables/filters. SR Master Fuse@861v8. Uptone Etherregen with 10MHz OCXO clock.