Hi I'm Marc from BCN3D Technologies.
I've printed with PVA some pieces like this one in my bcn3d+ with dual extruder: https://twitter.com/marcfelis/status/593790420754259968
The PVA is printed at 190-200 degrees celsius. We use Cura for print with dual extruder because Cura incorporates better options for dual extruder prints than Slic3r.
Another thing. When you assemble the dual extruder you have to calibrate the offset between the 2 extruders. The theorical offset is +52mm in X and in Y is +0mm. So you will put this offset in Cura (or Slic3r) and print some calibrate test. Seeing the print, you have to modify consequently the offset from the program and print another test till you will get the real offset of your dual extruder. So you will print like 5 test till you don't get the real offset.
In this link you have configurations with PLA + PVA and others: https://drive.google.com/a/fundaciocim. ... hIdGc#list
In this one, you have 2 important manuals. You should download number 1 and number 2. It's in spanish but probably you will understand it: https://drive.google.com/a/fundaciocim. ... hIdGc#list
Waiting for your feedback