I think you can benefit greatly be upgrading to the 661, if your still thinking about it. You can do 24 bit, the tekkeon can power it for 15+ hours, it has a s/pdif in and the XLR line-in has a pro line level of +4, so that should give lots of headroom.
Good to hear the bigbox works for you.
BTW, sent my specs (LB in a biggerbox case (2 XLR ins, 2 XLR outs)) into Jon, waiting for a response...