Thanks for the excellent response. She is a renter so I need to get the owner information. She did not request or demand I pay for flooring replacement. Ultimately I want to live and not whisper and slide across the floor and constantly worry about basic life sound... I can go to the HOA and get more information. This is my first condo/HOA experience and I've only been there for 3 weeks. Your response is greatly appreciated.

Also, is this not an effective intervention with no change to the ceiling?

http://www.kineticsnoise.com/arch/ultraquiet.html

If there is no movement by the HOA, I still have to do something for my own sanity. If the HOA doesn't do anything and I invest in this project alone, I'm going back to living a normal life and any future concerns can be addressed by the unit owner. I don't think that is unreasonable.

Sounds like if you do your part on your side, if they have a problem its their problem on their side. That looks like a good product.

Modifying a neighbors ceiling is probably not going to fly, it sounds impractical and may not work.

A floating floor is the right solution but can increase the cost of a floor by 2x to 4x. The product you linked looks good (if you can get it, looks like a professional product) but there may be other ways to install a floating floor. This is common practice in high end home theatre installations. basically you create an air gap (maybe filled with compliant materials like the product you linked) so the noise is trapped in that gap and transmits poorly to the real subfloor. One usually has to build another subfloor on top of the gap to lay the new flooring on. I suppose there may be some materials that allow you to skip the second floor step.

Do an Image search on "Soundproof Floating Floor" and you will see lots of options. Similar principals apply to walls where two layers of drywall with a gap are used.

I ran floor soundproofing search on home depot website and there were many products but none would be as effective as a true floating floor but might be worth looking at considering the potentially huge cost difference. If I went this way, I think I would choose the felt based product and use two layers rather than the foam products. there are designed for what you are trying to do and still be economical.

In the meantime, try carpet the main walking paths and key areas which should reduce the footfall noise your neighbor hears to a tolerable level.

Sounds like a new building to both of you or your neighbor should already be used to it.

True floating floors are crazy expensive and not worth it. You will have to raise the finished floor surface enough to get the isolators in. Most home theaters go with mass and absorption, when people start talking floating floors they are typically installing in-home studios, where sound isolation is incredibly important, rather than simply deadening the sound.

Seal openings + mass + resilient material = win.

Something is wrong if your neighbor can hear your conversations in a condo. Yelling and loud noises are one thing but people going to the bathroom and having a normal conversation are another. Make sure that you are fixing the right problem, you can spend a whole lot of money to fix a problem that doesn't really exist. My first instinct is that there are openings that the sound is traveling through and properly sealing openings may do more good than an expensive floor system.

Raising the floor an inch is not practical for an existing unit and it deals primarily with the impact noise. If your neighbor can hear you talking there are major sound leaks between floors. Your first step is to find them and seal them. Look for penetrations like for plumbing and recessed lighting below. Find out what other units have done about this problem.

Adding a layer of drywall on resilient channels on the ceiling below will be a fraction of the cost of adding underlayment to the floor and much more effective.

Since the solution will be expensive you should hire an acoustic consultant and present that advice to your neighbor.

The first step in problem solving is to define the problem and to do that you should first look at the original construction drawings at the building department. Make a copy of the floor/ceiling assembly drawing or specification and post it here; even a photo of it will do. Then take a look at your neighbor's ceiling while someone walks and talks in your unit. Look for obvious penetrations and determine what rooms have the worst noise issues. A consultant would be helpful in doing this.

Links:

Canadian research report contains details of the use of RC-1 resilient channels and the actual tested performance in STC and IIC values.

Noise Control in Multi-family Residential Buildings contains advice and a very complete list of noise barrier products.

I used to live in a condo which was built in the 1920s. It had a floating floor which was really a second set of floor joists not touching the joists in the ceiling below. It was original construction, and it made the ceiling-to-floor thickness twice normal. However, it was very effective - my downstairs neighbors didn't even know I played the piano!