She's not exactly showering him with kisses, but she's not backing away in terror any more--in fact, she'll pass within a few feet of him (with much growling) and will turn her back on him, and can watch him from ten feet with only an occasional hiss. (Athena is the only cat I know that occasionally hisses wrong and snorts instead. Then she coughs and looks faintly embarassed, and it takes a minute to get the hiss started again. Hissing is apparently like drinking milk--sometimes it accidentally comes out your nose.)
I hadn't planned to let them in contact this soon, but I opened the studio door and found Athena right there. Ben promptly fell over on his side--"Auggh! They got me, pardner!"--and Athena glared and hissed, walked off, came back to make sure he was still there for her to disdain, hissed again, and stormed downstairs in a huff. She was much calmer than she had been when watching him through the door, though, and after a few minutes, I think I figured it out.
See, from Ben's point of view, he's just trying to get out the closed door into the fun and interesting house. From Athena's point of view, however, a strange enemy cat twice her size is pawing his way through the door to get at her. She must have thought she was in a kitty version of The Shining, and her humans, who are so valiant about slaying wicked bugs and disposing of mice when they cease to be amusing, for some reason weren't doing anything. No wonder she was freaked out.
Once they were allowed to meet on her turf, where she was in her Happy Place (i.e. James's chair) she calmed down a lot. Ben's tendency to mostly ignore her, and if cornered, fall over on his side and look off in another direction, seems to help. She still growls if he moves in her general direction, but she's not spastic.
We'll keep seperating them at night, and when I'm not able to keep an eye on them, but it's a good first step.