So I have these LOTR BD images, I completely forgot these were mixed in the awful 6.1 format. A bridge to 7.1 which btw is garbage unless you have a truly massive room for that extra pair of floor standers / amps. Anyways, my setup is 5.1 (Well 5.2 but I don't have unique sub outs yet), and I'm stuck with all these 6.1 films. JRiver's auto up / down mixer on leaves me with an empty rear right channel. The only thing I can do is turn off up/down mixing to get sound coming from both rear channels, however I must assume that the rear speaker (of 6.1) is just being discarded. Its not the biggest issue but pans / some effects in the mix are definitely missing that middle part when it 'swoops' around.
I could copy whatever is in that rear channel to the SR and SL speakers using the parametric EQ however I can't for the life of me FIND that rear channel in my channel configuration (I've tried the back 2 channels of 7.1 which I kinda assumed that at least one would be that rear but its not).
Any ideas how to mix that 6.1 rear into my surround speakers?
There's a couple things going on in your post that I'm not sure about, but let me take a stab:
First, what's your channel output setting in output format? If it's "5.1," then you won't be able to access the rear speaker in PEQ because JRiver is only outputting 6 channels (meaning any channels above that are not accessible in PEQ, even if it looks like they are). If you want to do manual mixing, you need to choose "source number of channels," "5.1 in a 7.1 channel container," or one of the higher channel count options. 5.1 in a 7.1 container is preferable as it will maintain 5.1 as the JRSS mixing target for other content. You mentioned bi-amping in another thread, so I didn't want to make assumptions (I also bi-amp, which makes my channel configuration unusual). But once you've got the channels lined up, you should be able to use PEQ to fix the problem.
Second, you refer to hearing sound from "both rear channels" in a 5.1 setup, which is a little confusing. To make sure we're not talking past each other: the standard nomenclature (that JRiver also uses) is Surround Left, Surround Right, Rear Left, and Rear Right. SL and SR are present in 5.1 and 7.1; RL and RR are only present in 7.1 (the single rear from 6.1 is usually on RL). The reason this is important is that the
channel ordering is different in 5.1 and 7.1. The channel order for 5.1 is L, R, C, LFE, SL, SR. In 7.1 it's L, R, C, LFE, RL, RR, SL, SR. That means that if you switch to 7.1 output without reordering the channels, the rear channels will be coming out of the surrounds and vice versa.
I mention this because the channel reordering could explain why you're only getting sound out of "one side" with the 6.1 content: you may just be hearing the single rear channel coming out of the speaker you normally hear SL out of because the channel ordering is different (and RR is blank, because it's 6.1, so you hear nothing out of the speaker normally playing SR). You can also try reordering the channels in PEQ and see if that fixes it.
But if you could confirm your channel settings in output format I can offer more specific suggestions.