I just tried your procedure using the latest Ambeo VST3 and WL 9.5.40 with the same montage setup, and when I transferred the plugin to the montage, it said it wasn’t compatible, and left it unconnected, as was my previous experience.
Right now I’m just hoping that WL10 will be the magic point at which true multichannel processing appears in WaveLab; but I’ve been disappointed before. However, two other programs have gone from stereo to multichannel in recent updates (SpectraLayers Pro v4 and RX7), so it can happen.
Paul