Hello everyone, I'm a complete noob to this hoping to get some input from you. I'm getting 6'' engineered hardwood installed (Nail down With Glue Assist), my hardwood guy is telling me to get wax paper as the underlayment but I was told you don't need any underlayment for glue down with nail assist. What do you think? Just hoping to get some sound insulation and prevent squeaking.

Product Name 6" Oak Natural
Dimension 161mm/18mm/2mm
Wear Layer 2mm
Core Multilayer Bailtic Birch Plywood
Surface Wire Brushed
Anti Abrasion 7 ply polyurethane coating with Aluminum Oxide Finish
Joint System Tongue and Groove
Installation Method Nail down With Glue Assist

The wax paper may be called Aquabar. If you are using this and want to have glue assist you will need to glue the wax paper down so you could glue to the paper. I have never heard of this before. Usually with glue assist you glue directly to the sub-floor or a special underlayment made for glue assist jobs.
If you use a special glue with trowel spread you will not need to use a moisture mitigating layer of Aquabar.