How do I approach this

I've been with my lovely girl for 4 years, and I must say that I'm very happy. However, she is very conservative when it comes to sex, and I am a little; actually allot more experimental. Thing have started to get very routine, almost becoming boring. I have spoken to her about this and to her credit she did try to spice things up by becoming a little more vocal, but that’s about as far as she is willing to push the envelope. Unfortunately I've started to discretely look elsewhere, I haven't acted on it but I'm really turned on by the thought of being with other Women/Couple - which brought me to this site. So: 1. Have you ever been in this situation, and what was your partners’ response when you recommended "expanding the horizons?" 2. How do I approach this without making her feel insecure? 3. Or do I do this discreetly in a "what she doesn't know won't hurt her" kind of way. Cheers guys, any advice would be appreciated - Chap