A very good question. I remember having to deal with the wrath of Eden's owner in 2006 when a certain very well known DJ, who was doing Dusted for us played at Mambo for Tong earlier in the evening. The Eden/Mambo relationship is so poor that they weren't going to let him play at Eden when they found.
Luckily, my dilpomatic skills won the day and he did play, although he was hammered by the time I'd sorted it all out and he went on!
Having said that getting Tong is such a coup, he's prolly named his own terms and demanded being able to do Mambo. Given that Mambo have a strong tie-in with Pacha, selling tickets and doing pre-parties, it'll be interesting. Will Tong be pushing his Eden party while doing the ES from Mambo, while Mambo do a pre-party for Pacha's Friday night party