- Mbox does not support simultaneous use of the analog and digital inputs (4 discrete inputs)- Mbox does not support the "Low Latency Monitoring"feature in Pro Tools (though the unit itself offers zero-latency monitoring); and Mbox does not have a 128 buffer setting in the Buffer Size pull down in Pro Tools LE. - Although the MBox is equipped with 2 discreet, TRS inserts, it is impossible to run a hardware insert while playing back in Pro Tools. The inserts on the MBox are placed between the Mic Pre's/Line Inputs and the A/D Converters. Therefore, they are designed to be used while tracking only (this allows us to eliminate latency)."S/PDIF Mirroring" is always active (so there's only one Stereo output choice... "Analog-S/PDIF 1-2". The inputs are switchable via the Hardware Setup and Session Setup Window in addition to a separate Sync Mode option (Analog and Digital). Therefore, you can access the Analog I/O of the MBox while resolving to an external S/PDIF clock source.