Yeah. You'll need a small mixer and output. I like the NE Xerest Pola for compactness, mute switches, and headphone out, but there are a lot of good options. I love all the NE stuff!
You'll also want a trigger or gate sequencer to power those envelopes. NE has a lot of options for those, the Bin-seq is only 4HP wide as a gate sequencer. Probably you'll want a small sequencer too, maybe shop for one that has a built-in quantizer (O+C can do that, for example).
I happen to have a 220HP 7U case and I keep my DFAM inside the case... it's basically the center of my rack and I patch it to everything, so it didn't make sense to pull it away and have 10 cables of spaghetti between the DFAM and the rest of the rack. If I were you I would eye a slightly larger rack space with the thought that basically one row is already spent on your DFAM and Erebus. In larger racks power consumption is the biggest limitation, and the DFAM/Erebus don't draw as much power per HP as a lot of tiny digital modules, so it works out well actually.