I have SWN - Its a very deep and versetaile module, that can stand by its own.
It has sequencer and modulation + chords on bord, so u wouldnt need a external sequencer.
Its very complex and deep
its wavetable and spreads in 6 voices
SWN is amazing - but as I read your comment im not certain if SWN or Spectraphon are what youre searching for.
Maybe just pick a more simple voice for layering?
Or what about 4ms ensemble osc? - I think it could be a good addition, and easier to control.
If you get the swn, I guess it will be more like a replacment than a addition to the drone grone.
I had the SWN in my main case - but I prefer to have it in a small rack to focus on it.
You can spend hours only using the SWN.
You can do drones, melodies, chord riffs, endless timbress to explore
As far I know, the Spectraphon is more to make new sounds of existing sounds.
Greetings
Chris