You're right on there - communication within a relationship is essential to the health of the coupling.
jynxa, I didn't get the impression that your man is a shy person talking about the relationship between the two of you, but that he shuts down on the discussions specifically dealing with you wanting to participate in the larger community. (Please correct me if I'm wrong, this is just my impression.) Although I didn't sense any outright accusatory overtones in your approach to this or to him, it's clear that you think he's missing out and is not partaking in activities that would be good for him. Subtle as that attitude may be, perhaps that's coming across to him as you thinking he's "wrong" or there's something "silly" or "stupid" about the fact that it's not really his cup of sadistic tea. Perhaps he feels that he has to defend what seems like to him a perfectly rational attitude, and no one likes to have to play on the defense.
Perhaps take a different approach with him and instead of asking questions or launching conversations that nudge him into the BDSM collective, ask him how he would like to approach more intricate rope bondage, or what his suggestions are to furthering your sexual activities. What does he come up with?