I just installed the 5.5 beta (OS X). When I route signals through the H8000FW there is an increase in output levels. It is easily apparent; I'd say it is about +3db. All the input and output levels on the H8000FW are set to 0.0 dB.
My setup lets me switch my signal routing to the H8000FW, as necessary, so it is easy for me to A/B it. Nothing else in my setup changed, and I've carefully inspected the input/output levels on my other gear and they are all set to 0 dB. I'm sending signal in and out on the AES inputs from a Prism Orpheus. No Firewire cable connected.
Thanks for checking this out.