I do all my arranging in FruityLoops- I'll create all my synth tracks or electro drums or whatever samples I need, and then I'll export them in a .wav file and then just open them in CEP. If I need a guide track (scratch vocal, rhythm guitar, drummix) you can now load one up in FL Studio (Fruityloops 4.0) Which is cool. You can also use this feature (and FL's .wav editor) to add subtle VST effects to your tracks and then open them back up in CEP. I know you can use a VST-wrapper, but not all my freeware VST effects will work with a wrapper.
I don't know about syncing. I think maybe Dobro had tried this, but Im not gonna waste the CPU power on having both apps running at once. If you need record outboard synths/samplers with cpu midi files, either use FL's little audio recording, or open up the MIDI file with CEP, and have it play back in sync.
I know it seems a bit cumbersome, but its actually really really easy, and its never interrupted my creative flow.
Good Luck
Chris