I have not used cork, so I can't speak about that. I have used many other underlayments including FloorMuffler. In my personal experience Sound Solutions underlayment is the best for what you are asking about. One person can't hardly lift and carry a 6ft wide roll of this. Three things you need to have to achieve a quiet and fairly solid feeling floating floor. The substrate has to flat,flat,flat. Use a premium underlayment. Pick a quality floor with excellent milling and a stout joinery system, and the thicker it is the better imo. I have installed this way before and it is very solid feeling underfoot. Most folks are surprised when they discover it's a floating floor.

Ignore this post. It is a repeat which reposted when I used the back button on my browser.

Laurie, what flooring did you choose? I am also interested in more information on the underlayment for an engineered wood floor. I am still deciding but must wait to do my wood floor now after my tax season since I am now so behind from finally just about finishing the tile job. My job entails moving a lot of heavy office furniture with files in the cabinets so it unfortunately looks like the job may have to wait and I will have to keep steam cleaning the very light beige carpet every 3 weeks.

Oh dear. Noise abatement requirements with hard surface flooring over light weight concrete (aka "gypcrete"). And you only have enough room for 6mm worth of acoustic insulation. Hmmmm. You are getting into expensive territory. First check what is ALLOWED by the HOA/Condo board. They will have ratings that will tell you what you have to MEET or exceed with hard coverings. Secondly check to see if the acoustic glue underlayments will even grab gypcrete. Most things HATE gypcrete. I mean HATE. There are many high-quality glues that do NOT grab gypcrete. And the one's that do, can be nasty. But don't worry. Being in California means you can't purchase anything that violates CARB compliance - unless you order it over the internet (ahem...best to stick with brick and mortar point of purchase for stuff like this). And just for fun, not all wood floors can be floated and not all can be glued. And not all glues grab gypcrete...see where we are going here? And then there is the noise abatement that MUST be addressed BEFORE you go any further. Without those numbers, you are flying blind and so are we. In the cork industry, I NEVER got my 6mm cork underlay to pass a SoCal condo boards requirements. My customers ALWAYS had to go 12mm with a wood floor (of any kind). You can get some decent sound reduction with mass loaded vinyl. But it is expensive. It is very thin and very expensive. And vinyl does NOT like sitting underneath wood. But it depends on the mass loaded vinyl product. And QuietWalk Plus is a product that is relatively thin and yet has some of the same acoustic insulation as 12mm cork underlay. It will save you the height at least. It too is not cheap. https://www.mpglobalproducts.com/flooring-underlayment/products/quietwalk-plus/sound-rating/