I don't have a Mac, but I presume the DSP panel is similar. Try setting up a zone and using a parametrique equalizer filter ... (this was posted in another thread, so I'm just copy/pasting from MWillems
Maybe you can make it think that the sub is surround right by doing this ..
It's been discussed before, but there's currently no way to rename them. You can change the order using the "order channels" filter, which can be helpful. The default order of the channels is different in 5.1 and 7.1 because that's the standard. In 5.1 the channels are 0=L, 1=R, 2=C, 3=S, 4=SL, 5=SR. In 7.1 the channels are 0=L, 1=R, 2=C, 3=S, 4=RL, 5=RR, 6=SL, 7=SR.
Not sure if JRiver is "wrongly allocating" this or if the "publishing label" didn't have their heads wedged, not following standard practices. You could try different output settings like the 5.1 and 4 channel, but I presume you have played with those already.
(btw, I thought the sub channel was always channel 3, but I could be wrong about that one?)