Logic Pro x, a 64 bit app requiring OSX 10.8.4 introduces new routing options for rewire apps.

Reason 6.0 is required for 64bit computability.

1. Launch Logic Pro X.
2. Launch Reason
2a. Reason should launch into 64 bit (rewire 1.8.1) mode – as indicated in the master routing section.
3. Set-up your Reason interments or channels.
3a. Give each instrument a unique name distinct from it’s mixer channel.
3b. Route your instruments to individual “hardware” channels (1-64 in stereo pairs) in Reason.
4. In Logic X, create an External Midi, and a Summing “Folder Stack” set of channels for each instrument or mix group to be routed FROM Reason.
4a. The option to route audio internally FROM Reasons “hardware bus” is only available to Logic’s Summing -Sub tracks.

With this set-up you can play and record Midi data in Logic, while the datas triggers a software synth in Reason, then route the audio back to Logic to a summed track for recording or bouncing the audio output.

A bit of a workaround, but workable.