I figure since it's a floating floor to begin with, there's no real reason the underlayment so your choices are glue everything down.
Glue Down Flooring Underlayment. Gluing down plywood underlayment affixes it very firmly to the floor. It mentions 'cork underlayment adhesive'.
Tranquility Ultra Underlayment Specifications Lumber Liquidators Flooring Co from www.lumberliquidators.com
You couldn't move these boards with a sledgehammer! Those nails seem a little long to hold down something that thin. My floor is ¾ tongue & groove with.200 thick (13/64?) underlayment over it.
If you glue down your hardwood, then you glue down the cork underlayment.
1/8 thick underlayment and moisture barrier for kahrs flooring or any engineered hardwood or bamboo flooring. You might be tempted to do this, but almost all underlayments are a floating system with adhesive. Many people don't bother to glue down their plywood underlayment. Click lock floor over 3 in 1 underlayment.
