I think the key word is "floating". This isn't a floating floor, it's a naildown. I don't believe it's going to be nearly as effective in a naildown situation, as most of the noise that is "muffled" in a floating situation is from the fact that there isn't good solid contact with the subflooring, as in nailed down. WHen there is good solid contact with a subfloor, the majority of the noise produced is from the reflective (rather than absorbtive) nature of the hardwood surface itself. Sound just echoes more into the air from a hardwood floor than it does from a sound absorbtive carpet floor. No amount of underlayment is going to alter the nature of the sound echo produced because the flooring is a hard floor product and not a textile based flooring product. It may be possible that installing a manufacture approved for naildown installation sound barrier can help with some of the percussive sound transmission from floor to floor, but it'll never be as quiet downstairs as if carpet on padding was the second floor material. And, you'll still get sound echoes upstairs that travel through the walls and open areas, simply because the wood surface reflects sound. You can't alter the basic nature of a hardwood floor. You can use rugs and additional soft furnishings to moderate the sound absorbtive properties and mitigate some of that reflectivity, but you'd have to practically cover all of the rooms wall to wall with rugs to make it be as quiet as carpet could be.

Invented installs can be risky. I once recommended a customer use cementious backer panels to inexpensively raise the level of a room prior to installing a laminate floating floor and it worked perfectly. The key to success with any floor installed over concrete is to maintain moisture vapor transmission from the slab at acceptable levels. If the recommendation was from an experienced floor person and this person knows about moisture vapor transmission and how to control it, then I would not dismiss the recommendation out of hand.

First, I would properly test the concrete for moisture vapor emissions(vapors cannot be seen or felt) I would then flatten the concrete substrate to the strict manufactures specification of 1/8" in 6 feet, Some, like Owens Plank, is 1/8" in 8 feet. Use a straight edge 8 feet or longer to varify. A stretched string line can also be used, to tell you where you need to grind down the high spots first, and fill the low spots. Now your substrate is prepped, you may need a troweled on moisture barrier membrane, if the concrete tested high for moisture vapor emissions. Following the directions to the letter. Now, all the doorjambs need to be undercut, so the flooring slides beneath them. It looks hacked in when I see someone try to cut around door jambs and trim it out with shoe molding... TACKY!!! Now, find your longest straight wall in which you plan on starting from. On both ends of the starting wall, dry lay about 4 or 5 rows, if it is plank flooring, and about 10 if it is strip flooring. And push them up to the wall and adjust for your expansion gap. Make a mark on the substrate. Do the same on the other end of the room. Now pop a string chaulk line, between your marks. That is your straight, and square starting line. Now, trowel out your glue, making sure you have a rag with mineral spirits on it, handy to wipe fingers and any smudges of glue(this is where most pros and DIY'er mess up and get glue everywhere) Spread/comb out, the adhesive, not leaving any big blobs, not going over your popped line. Don't get so much glue spread down your run, that it sets up before you get wood into it. Since this is your first time, about 10 feet spread in your popped run at a time, and then finish spreading the area, when you get down there to it, and can't go any farther until you do. Work your way from your line back to the wall, using blue tape, to keep it all tight. Once you get that band completed. Measure out so you can pop another line, but this line is just a glue control line. Measure out about 2-3 feet at a time, so you can reach across or jump across your spread glue, if needed. Once you get going, production will go faster.

Cork, as I mentioned in the earlier thread, does not need to be glued. It can be floated. That means it just sits there. Doing nothing. Minding it's own business. An engineered hardwood that is DESIGNED to be floated (must state on the installation instructions) can then be floated over top. The tongue/groove is glued (a line of glue is applied to the tongue/groove) and then pushed together. You wipe up any excess glue and then move on to the next plank. Some blue tape is then used to hold the planks together while the glue cures. It takes about a day. Once you the glue is cured, you have a fully functional floating engineered hardwood floor. Done. It is MUCH CHEAPER and much faster (almost half) than adding new sheathing and then gluing/stapling the hardwood. Whether or not you can float/staple will be clearly notated on the installation instructions.