In order to use Renoise’s “Render Song To Disk” feature to produce stems, the “Save each track into a separate file” isn’t very useful since it renders each track isolated from effects added to groups and sends that track is a part of.
While that sort of 100% dry rendering may be useful to some, I would expect most people to find it more useful that each track is rendered as though it was soloed in Renoise, with parent groups, sends, etc., and all of their effects active.
It would still not become 100% perfect due to Signal Follower and other interdependent track effects being disabled, but independent effects such as compression, EQ and reverb would still be applied, making the render much more useful as a stem.
I’ve searched, but not been able to find a plugin that does this.
I’m assuming the behavior you’re describing is with sends that are set to “keep source”. With “mute source” I think you get a single wet stem from the send track.
I haven’t tested this, but could you use another pair of sends to get the behavior you’re after?
For example, let’s say you have track01 and a send to s01 — when you render these stems, you get track01 dry and s01 wet.
If you would prefer to have a single stem wet, could you add a second send on track01 sending to s02 and a new send on s01 also going to s02, both with “keep source” set? This seems a bit convoluted, but it’s just a mixer after all.