Native Instruments has updated Guitar Rig to v2.2.2. This update fixes the "no output" issue. The release notes state:
- Universal Binaries Update: Now compatible with Intel Macintosh Computer.
- FixedComponents.fcf issue fixed. Under certain circumstances this led to a burst error overload or silence when using Guitar Rig in a host.
Native Instruments also appears to have updated the Windows versions of Pro-53 (v3.0.4), Spektral Delay (v1.6.0) and Vokator (v1.2.0), bringing their version numbers in line with the Mac versions (presumably they contain unspecified bug fixes; the release notes suggest you will need to reauthorize after updating).