Yes, it is possible with Jack!
First you need to go to the settings/preferences, audio, if you have jack running you can config how many in/out channels you want, up to 64 each.
To loop audio out of renoise, you need to output a track (or send) to a channel pair. In the mixer there should be a drop down menu at the bottom (it can be enabled/disabled with the lowest icon to the far right of the mixer tab, which looks like an arrow to a dot "-->o "). This is normally set to "Master" routing each track to the Master channel, and the master to outputs 0/1. You can route any channel to such an output, it will be directed to the jack ports of renoise.
To loop audio back in, you need the "#line input" device somewhere in a track. You select the input channel pair, which will also correspond to jack channels, and it will insert the audio.
Not sure about latency implications right now, so if a backlink will add a buffer period of latency or not.
Hope that helps.