eXT2 is not recommended with Renoise. It is buggy and have synch problems.
Go for eXT v 1.41
You can read about some of the things you can do with this combo in this thread.
Btw, after that thread was made Renoise got the Line-In device.
If you put that device in front of eXT vst version, then you can record directly into eXT that can then be synched to Renoise.
So eXT is useful to record/stream,/playback large files synched to renoise,
You can route things as you want. Bundle fx’s or instruments. Use midi plugins,
Use Pianoroll and many more things. A very nice tool together with Renoise.