From the Tascam site (retrieved 2014-02-06):
The DA-40 builds on the feature set from the DA-20mkII, adding functions that professionals depend on.
SCMS codes are totally controlled on the DA-40. You can select what SCMS status you want to write to the DAT, depending on where the DAT is being sent.
For cueing purposes, 2 locate points are added, allowing direct locate capabilities even if there is no track ID at that location. Additionally, the single play function is ideal for live environments. It allows the engineer to cue in one track and forget about the machine - it automatically sets itself at the next cue. For presentation and on-air applications, this is very useful since the machine won't accidentally roll into the next cue on the DAT.
Another handy function on the DA-40 is the ability to read and write track names. The track name will show up on the DA-40's text screen for easy reading. Track names make it immediately obvious which cue you are listening to. This is especially handy when dealing with multiple mixes of the same material, like the same ad spot with different regional specials, or multiple mixes of a jingle.
The DA-40 has balanced XLR and AES/EBU connections, for easier integration into professional set-ups. The analog in ports can be switched to calibrated so that the input level controls are overridden (thus controlling the level from the console), and the outputs have attenuation pots for fine-tuning your connections.
There are numerous remote control possibilities. The Parallel I/O port allows simple remotes and tallies from automated control systems, or broadcast consoles. Two pins in the Parallel I/O provide a serial port for basic serial in control. The optional RC-D45 remote is also designed to work with the DA-40.