HDFury boxes do absolutely nothing to the audio stream apart from split it from the incoming (or EARC) and pass it to the processor audio output as HDMI 1.4 matrixed into a blank video signal. You have to configure your source to send what is palatable to your Meridian processor. If your player can't do the unpack and send LPCM multichanel, you won't hear it.
Don't know about the ROKU, but by manipulating the EDID data in the HDFURY you can get an amazon fireTV to send LPCM even though it's not a configurable option in the FireTV. Probably worth a try.
It would be great if someone would produce a black box that simply took in DD+ and higher bitstream on HDMI and split the channels out to 6 or 8 LPCM on HDMI, but I've not found anything that can actually guarantee to do that. In the Meridian Architecture this could only be done by a significant enhancement to the HD722 - there's not enough bandwidth in one SPDIF connection to send a DD+ bitstream to a Meridian Processor to decode.

Lounge: G61RSL, DSP3200, DSP3300, DSW, HD621+Vertex2, SBT, Kef Ci160.
Office: DSP33, D1500, SBT
Archive: 568.2m, 562v3, 562v, DSP3100