Please help.  I know there must be an answer to this but I just can't think how.

In a nutshell, I would like to hang a second digital output off my Fireface 800.

Let me explain step by step:

In my studio the control room and vocal booth are one and the same.  So when I am recording my vocals, naturally I need to make sure that the mic output is not fed to the monitor speakers.  No problem. 

I monitor playback through my FF800 into a Lavry Black DA10 which I feed via the optical output on the FF.  Great.

When I'm tracking, it's then a case of routing the output of the mic to the Lavry (which has a decent headphone amp) while turning down the monitor speakers.  Simple, but when you're doing the same thing a hundred times a day, then it's a pain.  So in practice what I do is permanently route the output of the mic to the headphones out on the FF.  So my cans in the booth area are always live and I'm not getting feedback because the mic is not routed to the momitor speakers.  With me?

Ok, I want to refine this set-up.

While the headphone amp of the FF is ok, it's not really up to the task of critical listening.  However I happen to have an original Benchmark DAC1 here with a really stellar headphone amp.  This is what I'd like to use for tracking. Trouble is that the FF digital outputs run in parallel.  So I can't set up a seperate routing to feed the coaxial and the optical outs.  They carry the same signal as each other.  Ideally I'd have the mic output going off to the Benchmark permanently via the co-axial out, but then have the mic output muted from my main outputs to the Lavry.  But that won't work.

So the short question is, can I find a way to feed another seperate digital output to my second D/A device without sending the same signal to my speaker monitor outputs?  I suspect there may be a hardware solution but it's beyond my expertise.

I know this is a bit of a long winded question and there must be a simpler way to explain my problem, but thanks for sticking with me.  I grew up in an age that was firmly analog and the whole area of digital routing is a bit of a mystery to me!

Thanks!