You don't say your wifes age, but I'm assuming she is the same age as you. You also don't say how long you have been married but I'm guessing just a couple of years or so.
You need to give this time. She is newly married, and you're talking about opening up your sex life to bring others into it. Wake up man! give her time to feel secure in her life with you, without the background fear that you are looking to replace her. She's young yet, she may have a different view in 5 years time.
Also, if you do persist in pursuing this idea then focus on bringing another man into your lives, put off bringing in women, who she will see as competition, until you have her hooked on having an extra man on call.
You need to decide just how selfish you want to be and whether you are in this for the long term, because buddy, it's going to take a long time and lots of patience on your part.