I'm not 100% sure about asio in win7 64-bit although my experience with Sonar has been very good; could be a Steinberg issue (as usual). AFAIK, the WASAPI protocol should have addressed any timing issues with win7.
I'm not sure about recording the drum machine although it will work. However, unless you start on the bar:beat, editing can be a problem. Slave the drum machine to Cubase to eliminate midi sync issues, but try recording audio of the click for the duration of the song then see if it lines up with the grid. (I hope I explained that right)