Notion 6 currently sends midi over rewire (part of the props rewire spec). Unfortunately Sonar currently does not enable or use Midi over rewire. Implementing this would facilitate the use of 3rd party notation applications like notion 6 in Sonar, and potentially address some of the concerns about staff view limitations, by allowing users to have midi in the notation instrument play through their Sonar based soft synths.

Thank you Brando.  I was going to put that one in myself.  Looks like Sonar will send MIDI out but not accept it in via rewire.  I'm not a programmer, but seems like implementing bidirectional rewire MIDI would be simpler than bringing the notation aspects of Sonar up to Notion 6 at minimum.  While Notion 6 is not at the level of Finale or Sibelius, it is light years ahead of the Sonar notation and quite affordable.

You could use virtual midi cables in the mean time . I do with sonar and Sibelius .

I do use Loopbe1 between Notion and Sonar and some of the issue is with Notion too.  While Loopbe1 allows 16 channels, for my work, those channels are taken up with different patches on one instrument.  I use Loopbe1 to bring the midi into Sonar because Sonar is much better at tweaking the midi data than Notion but Notion is far superior than Sonar at entering the raw note data.  I would spring the $20 for Loopbe full but Notion only allows 4 midi out ports whereas via rewire it allows 16 midi out busses with 16 channels each.  I still might get the full Loopbe as it would improve that aspect of the workflow 4x currently.
 
I have read on the interwebs that Reaper (verified in their user guide) and Cubase can bring in midi via rewire.  It may not be a big thing now, but I bet as time goes on it get implemented more in the competition.