I did get a KPD+SPD Victory but involved going for a Civil War Victory. My strategy there was to focus on party stuff and keep on expanding and militarizing the Reichsbanner and trying to fix relations with the KPD. I then gave Thalmann the chancellorship and fought with the KPD, with the rather amusing thing where the Reichsbanner outnumbers and outmilitarizes the other paramilitaries and the state's armed forces. That run ended with Thalmann trying to remake Wiemar Germany in the Soviet Image.