HVAC guy is finished. Ended up increasing my original quote by a little over $2k. Sure hope it was worth it. He built me 3 muffler boxes with internal baffles and lined with Mason Akousti-Liner R. He wasn't able to test with deep base but the 3 octaves 500hz and up he tested showed a 20db drop. Add the Thermoflex MKE and regular flex vent and I'll hopefully see a 30dB or more decrease through the ducts. He also built a custom cold air return box lined and with alternating baffles of Mason Akousti-Liner R above and below the hole into the main duct.