Thanks for responding.
Their product is here: http://www.presonus.com/products/Detail.aspx?ProductId=3
The Presonus people have not gotten back to me yet, but this isn't particularly unusual (unfortunately). According to their documentation – as far as I can tell – it's the same firewire set-up as the Harmonizer regarding chaining devices.
I will double check both ports on both units to make sure they are both functional when I hit this problem hard again tonight. I may end up just replacing the Presonus unit with something like a Apogee Rosetta 800 with a firewire option card or an RME Fireface 800. Do you have any users successfully using the RME device and the 8000 chained? Thanks!