TI Realtime rendering in Ableton

[mrvinyl]

I'm having problems rendering my track

I'm using an access virus TI external synth as my lead sound.
I know I have to basically realtime render (bounce) the midi track down to audio but when I do so the track is not in sync with the rest of my arrangment. realtime rendering is introducing some kind of latency which is a pain in the arse as I've got a squillion midi controllers going on as it is let alone having to worry about this.

why is it happening? can someone explain so I can get my head round this problem

thanks and merry christmas