Have used FL as vst multi-out in Reaper for beats, I love slicex.
Make a track preset of FL multi-out.
But when the arrangement is settled I prefer to render the FL tracks and get FL offline, just to make the project more stable for future use.
(Like most do with softsynths also)
Sometimes start songs in FL and then go to Reaper. I export synth midi so Reaper does the softsynths. FL the drumsamples and Slicex.
I learned a lot from using FL which I can also use in other DAWs.
Before that I played every track the whole song through, which for some tracks is still nice depending on the style.
do you use FLstudio in Reaper? How?
Linear Mode
