In ableton you just turn the channel off. it still registers a signal, it just doesnt make it to the master channel. So if FL's signal flow is the same, turning the channel off should still work, because your signal is going through all the compression before its being shut off.
Yep, silent sidechain as chev said. Every producer should be doing it. Either that or buy a compression plugin that has sidechaining presets like Vengeance Muiltiband or xFer LFO tool
Yeah man, I'll help you set up the Edirol FA 66. Steps: plug in power, turn onto to AC power, connec t firewire 800 from unit to macbook..... win. Literally that easy, apple's core audio just works it's magic