One problem I had with tying X up originally was that once he's bound, he pretty much can't pleasure me. I can make love to him, but his hands and his mouth are caught up, which limits a lot of what he can do. In addition, we're bound to pretty much one position. All of that can get a bit...dull. Sex needs to be about give and take and we need to make sure we vanillas get some of what we want as well.
Solution: untie him! Hear me out. I talked this through with X and have tried it and it works great. Start with basic make outs. Then tie him up in whatever fashion suits you. Play with him, tease him, and bring him as close to orgasm as possible without going over. Then unbind him and let the kindled passion assist the two of you in coitus/manual/oral/whatever you demand of your sub. Once you've gotten enough, retie him and finish him off in whatever fashion works for you.
Doing things this way not only makes sure you're both satisfied, but it also gives you a chance to play with more toys in a single session, keeping the interest going. Give it a shot!