I want my wife to cuckold me.

Hi, Im a 25 year old male. Ive been with my wife for six years. She was a virgin when we first started dating and I'm the only guy she's been with sexually. We done some kinky stuff (bondage, role playing, etc.) but never anything with other partners. I would love for her to cuckold me, but she doesn't want to. Ive offered for her to have sex with any guy she wants, but she still doesn't feel like its right. Im white with a 6 inch cock, its nothing special, and i want to watch her to experience a huge dick. Ive told her I'm down with anything, one guy, two, or a whole gangbang. Any advice on how to get her to come around?