there's nothing you need to do in Pulsar besides have an ASIO Source loaded before openeing Cubase. Once in Cubase go to the devices tab. There should be a Reason entry. Click that and the ReWire panel will pop up.
Things to make sure of:
Whatever you have routed to outputs in Reason will be reflected in Cubase, so if you're only using Mix outs in Reason, you'll only have 1 stereo channel to deal with. If you're using tons of channels (aside from the Mix out) you'll need to enable them all in the ReWire panel and then you can route them as desired.
I'm currently working on a project with 18 Reason outs into Cubase going to the STS 24ch mixer and I can use Pulsar AUX & Insert effects on different Rex loops, ReDrum kits, etc. It's a pretty bitchin combo, and it doesn't eat up too much CPU!
Hope that helps,
Sam
