this could compensate the ram limitation… ? export your tracks as 3 (or more) separate tracks each and import them into a big live session… etc… (off course, i’m suggesting this thinking about live acts… not for the final render of songs) and most of all, i’m 95% sure it’s impossible to do! 
But the audio stream within Renoise can NEVER use mp3 so that idea can just never work!!
Need disk streaming, no other way about it.
:)99.9% now
Then why suggesting it?
hmmm, who knows? maybe because of the 0.01%? 