Green glue (which is not a glue) should offer (roughly) 18 dB worth of acoustic insulation. The rubber will offer another 12 dB or so. One person's "floor" is another person's ceiling. To be clear, many "wood frame multiple family units" have a subfloor that is "worth" 35-40 dB. Start looking at your numbers to see how some of this stuff compares:
1) Green Glue sandwiched between plywood = 18 dB (requires the screw holes to receive the isolating foam/caulking)
2) 1/4" rubber (which can off-gass for years) = 12-15 dB
2b) Careful with the rubber underaly...Coretec does NOT allow this material nor this thickness...you may have to sandwich the rubber between plywood
3) Roxul between the joists: 5-10 dB
4) Regular drywall on the ceiling: 5 dB
If you add up your basics: 40 - 48 dB You are WELL INSIDE the 'acceptable' for subfloor acoustics for a wood frame multifamly unit building.
Acoustic drywall (5/8") will offer another 18 dB. If you replace the regular drywall with 5/8" acoustic drywall ($3/sf) you will bring these numbers up to 55 - 63 dB.
If you wish to keep the old ceiling in place, you can add regular drywall (5/8") and use Green Glue between the two layers for 18 dB (works out to be $2/sf using regular drywall and green glue).
Remember: pot lighting = NOISY. Anything that breaks the acoustic ceiling, makes for a noising living situation on the lower level. Track lighting is a better option.
I HIGHLY recommend you check with CoreTec...that 1/4" rubber underlay may not be allowed. Sadly that removes 20%-30% of our acoustics...which is MASSIVE. Remove the rubber and substitute it for new drywall+green glue ceilings. It will be MUCH cheaper. That rubber is going to be $3-$4 per square foot....and it may not be allowed.
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soundproofing floor
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