Exactly that, Hadding.
The Feds never intended to have their fake tape ever subjected to any scrutiny other than to video tape his wife's reaction to hearing it *in their controlled room*.
After that, the original tape gets misplaced or lost somehow, but the video tape of his wife listening and reacting as to how "it kinda sounds like him, but ..." would be introduced as evidence with regards to her testimony ONLY. The Feds would make sure that when they played the tape for her, it would not be clear enough on the video recording they would be making to allow any decisive scrutiny (as to the copy they would be playing for her benefit). They only wanted to be able to introduce that video tape to make sure the jury knows that his own wife thought it "sounded like him".
Instead of not wanting to scrutinize that original tape, Ed is probably biting at the bit to get his own experts to go over it with a fine tooth comb. Ed also knows (provided he never actually had that conversation) that the Feds would have to disallow any outside scrutiny of that tape *AT ALL COST*, so, it was a bewilderment to him as to how they were going to ever get past that hurdle. It was when he realized that the AG had invited his wife for a private hearing, that he could put together their plan, and he wanted to make sure that the FEDS would not be able to use any aspect of that tape without allowing his own experts to have a go at it. Otherwise, why would he care how his wife reacted. Even if she denied it was his voice, the Feds could still introduce it, along with an army of experts to convince even the most skeptical juror, provided it was actually and genuinely a real original tape recording of an actual conversation as they were purporting it to be.
Ed would have gained NOTHING by having his wife deny the tape, if Ed knew he actually did have that conversation because he would know that his wife's denial wouldn't mean squat up against Fed experts to authenticate it.
The only explanation for Ed's instructions to his son and wife was that he saw through thier scheme and wanted to force them to either give up on the "tape", or let him subject it to a thorough analysis by his own experts. They will NEVER allow that, and Ed knows that, because he knows whether or not he actually had that conversation.
Don't you see, it is the veracity, or falsity, of that alleged conversation that makes, or breaks the Feds case.
The only way a person exercising critical thinking here can entertain the notion that Ed actually had that conversation is if the Feds let Ed's experts have a good go at the alleged ORIGINAL tape.
That ain't gonna' happen.