With the cats I've introduced I finally learned to just let them work it out. Of course I'd keep an eye on them until you are sure things are settled. With my guys I'd keep them apart when I wasn't at home to oversee things, especially when dealing with kittens/adults. I think Rumor hissed at Moxie and Decker for a solid year.

The main thing is to just introduce them slowly, make sure to give Taz lots of attention to cut down on jealousy and just let them make friends on their own terms.

Sounds like Taz is already doing well going into the same room and being more relax. I'll bet they'll be friends in no time (or in my cat's cases at least learn to coexist).