Using 2.6 on a PC with Sonar and I have no problems here. Arturia finally fixed a weird issue that was causing patches to save with different cabling than patched!
This might not be relevant to MAC, but perhaps you have Omni set on your MIDI channel routed to MMV... Try specifying MIDI channel 1. Maybe the plugin is more sensitive to incoming MIDI and it's causing it to slowdown needlessly.