At no point should nails penetrate the Iso-Step floor underlayment layer and make contact with the sub-floor. This would ‘short-circuit’ the flooring assembly and allow sound and vibration to transfer to the underlying construction assembly.
The nail-down flooring should be nailed to an additional subfloor layer. The subfloor layer should be thick enough so that nails do not protrude. The Iso-Step flooring underlayment would reside under this layer, free from any penetrating nails.