What if you filled the top torsion box with cement along with the bottom box (shelf)? Would that mass absorb the bulk of the resonances and for only a few bucks? Or even spray foam but the cement would provide both mass and weight which are both anti-resonance compatible? I love the dedication for completeness in your design effort and your inclination that a design can always be improved and accessorized. Why have a computer if all you do is play games on it, major kudos to you. Hope you the best in all you do. My machine sits on a poured concrete work bench and I think it is much quieter than any of the videos I’ve seen, One more question: What if you added a piece of sheet rubber (shower pan liner at Home Depot) between the parts before joining, decoupling the joint members to eliminate frequency transmission through the frame members and also MLV between the plywood and frame members. I made my own MLV using alum flashing and this sheet rubber, it was helpful and added about 20 decibles reduction to my enclosure. See how that works in your analysis efforts, I;d love to see those results. Terrific job with the modeling. Jude