I am going to put an engineered floor (Robina) in two upstairs bedrooms, hallway and laundry closet.

What's better to muffle sound - 1/4" cork or one of these 0.08" silencer mats? The silencer mat would be a product by Mirage (info http://www.miragefloors.com/pdf/Membrane-Ulti-mat-e.pdf) The tech specs for the mat are FIIC 63, though on 8" concrete - I called and they said they didn't test the acoustics over a wood floor, but its rated to go on wood.

These areas are over my kitchen & living room, so I want it as quiet as my budget can allow.

Subfloor is OSB on joists @ 16" centers. Flooring is 5" wide engineered random length planks, 1/2" thick, maple.

Many Thanks!

PS - I happen to already have 1/4" cork for 60% of the job.

PPS - The installer doesn't want to go with the cork as the nosing by the stairway won't be compatible with 1/4" cork and 1/2" flooring.

I'm partial to QuietWalk, but since you have 60% of the cork, seems like a no brainer. Is the nosing existing? Don't quite get the nosing problem. If existing, tear it out and through some 1/4"plywood under a new one, or install new the same way.

IIC ratings are geared (and required) for condo units. You description sounds like a private residence so sound dampening requirements are for you to decide.
The key is to make sure whatever underlayment you use is acceptable to the floor manufacturer's warantee requirements.
And yes, cork would be a good option in your case since you already have more than half of what you need.
Raise or replace the existing nosing.

pretty sure those ratings are also for a floating install. Dont think the same numbers apply to a nailed down floor. Ive known people to use it with a nailed down floor but just not sure how much that will alter the specs. I lived downstairs in my folks home way back when and we had wood floors covering the entire 1st floor. The only time it was loud is when my little brother wore his cowboy boots, it sounded like a spagetti western when he walked down the hall.