Answers

Unfortunately, insulation and sound proofing is not required per code between conditioned spaces in this case.

It is also worthy of note that additional insulation between the floor will do very little to impact the noise tranmission as a majority is carried via vibrations on the framing. 

There are applications and techiques that can can be deployed.  All of them will require removal of the existing ceiling if you stay with a drywall finish.  You can run resilient channel in addition to sound de-coupling isolators. 

It is not an easy or cheap bullet fix in this case. 

If you don't want to loose ceiling height, you will need to remove the celing covering to gain access to the floor joist cavities.

A product we've had great sucess with is Roxul (http://www.roxul.com/residential/create+a+quiet+home/which+safe+n+sound).

You might consider trying to add a new layer of ceiling drywall using GreenGlue sound proofing adheasive. This gets installed without removing anything too, it should be noted . This will be the most inexpensive aproach but may not be a complete cure. And you'll only lower the ceiling by about 5/8".

 You can look up Green Glue on the web for more info and where to to purchase.

Unfortunately I think WoW Home Solutions answered you correctly. This is an issue that should have been addressed in the planning phase by a forward thinking builder and/or architect, and at the latest in the building phase (assuming you had your home built; if it was a production tract home, then I'm sorry... and prepare yourself for more problems down the road....). Now that your home is completed, there is no easy or cheap remedy to this issue.

The only thing I can suggest that may work (emphasis on may/might/maybe) is to strip the existing drywall off the ceiling and replace it with soundboard. Insulate with spray foam (professional application) while it's all opened up. The spray foam will absorb some of the vibration and deaden the transfer of noise.