Should work but I would recommend using a FireWire 800 to 400 cable instead of the second adapter. That way you only need one adapter to thunderbolt.

Follow-up:  I tried this as you suggested, using a simple Firewire 800 to 400 cable instead of a second adapter.  But it did not work properly (see below).

But what DOES work is putting an actual FW 400 to 800 adapter (made by Elago, available on Amazon) in sequence between the Apple Thunderbolt 2/Firewire 800 adapter and a standard Firewire 400 cable.  So either my new FW 800->400 cable was bad or it needs more intelligence than a dumb cable.

FYI, here's what happened when the first configuration failed: 
TotalMix would seem to run but would not bring up any windows (I call it "lobotomized" TotalMix) and the Fireface Settings program would not run at all.  I've found over the years that this is typical behavior when the Fireface is not properly connected to the computer.  I've heard that these two programs actually run on the Fireface interface, not the computer (except for a stub), so lack of a connection would indeed lobotomize them.

My 12-year-old Fireface 400 is still running strong!

A FW400 to 800 "adapter" is just a cable. No electronics in there...

Could be the cable was on the edge and the TB2 to FW adapter added enough loss to push the combo over the edge?