The principal feature of the box is sum and difference (MS) processing for your 2-bus mix. This allows you to add a process such as EQ, compression or de-essing to the side channels without affecting the mid channel, or vice versa. The box then re-codes the returned M and S channels into L and R. Quite boring really, except that the Dangerous web site talks about an S&M matrix, which sounds a bit more interesting.

I wonder if Fab is using the D Master for inserts ( which would be redundant in my case because I have the MixDream which has inserts built in). What do you think Bos? I'm going to contact Bob at Dangerous I think.

I see using the D Master for mastering via my second mastering rig but it seems redundant for anything else if you already have an analog summing amp, yes?

No, not necessarily, unless your summing amp already has M-S processing. Some mix engineers like to play with the stereo image width at the 2-bus stage (e.g. bring low frequencies into the centre), and a box that has a pair of encoder-decoders gives an easy way of doing that. The Dangerous Master has a number of other frills (sorry, features) that are more relevant to a mastering process.

PS thanks for fixing the ampersand problem.