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[jjkale]

I would like to set a crossover of 400 Hz for my mains.  This is a 5.1 system with 2 subs.  Music only so bass management only, no LFE.  My mains are bi-amped with significant power.

Would this work?
Copy RF to U1, 0 gain
Copy LF to U1, 0 gain
LowPass 400 Hz U1 at 12dB/octave
Add U1 to Sub, 0 gain
High Pass RF/LF 400 Hz at 12 dB/octave

C/RS/LS use normal BM crossover set at 100 Hz, 12dB/24dB

All BM is now mono+summed and routed to miniDSP for independent alignment/eq on 2xSubs and L/R woofers.  I can further refine the high pass and low pass settings on miniDSP with REW measurements.
Finish it off with global EQ by Dirac Live.

Will this work?
Thanks very much.

[mwillems]

I would like to set a crossover of 400 Hz for my mains.  This is a 5.1 system with 2 subs.  Music only so bass management only, no LFE.  My mains are bi-amped with significant power.

Would this work?
Copy RF to U1, 0 gain
Copy LF to U1, 0 gain
LowPass 400 Hz U1 at 12dB/octave
Add U1 to Sub, 0 gain
High Pass RF/LF 400 Hz at 12 dB/octave

C/RS/LS use normal BM crossover set at 100 Hz, 12dB/24dB

All BM is now mono+summed and routed to miniDSP for independent alignment/eq on 2xSubs and L/R woofers.  I can further refine the high pass and low pass settings on miniDSP with REW measurements.
Finish it off with global EQ by Dirac Live.

Will this work?
Thanks very much.

That will be close to correct.  Suggestions:

1) In step two, you need to "add" LF to U1 instead of copying

2) You might want to reduce the gain of both RF and LF during the transfer so they'll sum flat (instead of +6dB), especially if it will be coming out of two subs eventually. 

3)You might also want to think twice about summing all information below 400Hz to mono, there's quite a lot of positional information below 400Hz and you've got two subs (you could send different channels to each).  To put it in perspective, middle C on a piano is 241Hz, so the entire left half of the piano will be in mono coming out of the subs (+ a few more keys to the right).  Just thought I'd throw that out there, you obviously know your system, and it may not be an issue for your setup.

4) JRiver's built in HPF and LPF are butterworths, so your proposed arrangement will have the usual 3dB "butterworth bump" at the crossover.  You can either eq it out, ot just cascade two 6dB HPFs and two 6dB LPFs to create a Linkwitz-Riley crossover at 400Hz, which will sum flat.

5) You'll also need to set your output format to a higher number of channels; you'll probably want something like "5.1 in a 7.1 channel container"; if you do go that route, you'll want to use RR or RL for mixing instead of U1.

[jjkale]

That will be close to correct.  Suggestions:

1) In step two, you need to "add" LF to U1 instead of copying

2) You might want to reduce the gain of both RF and LF during the transfer so they'll sum flat (instead of +6dB), especially if it will be coming out of two subs eventually. 

3)You might also want to think twice about summing all information below 400Hz to mono, there's quite a lot of positional information below 400Hz and you've got two subs (you could send different channels to each).  To put it in perspective, middle C on a piano is 241Hz, so the entire left half of the piano will be in mono coming out of the subs (+ a few more keys to the right).  Just thought I'd throw that out there, you obviously know your system, and it may not be an issue for your setup.

4) JRiver's built in HPF and LPF are butterworths, so your proposed arrangement will have the usual 3dB "butterworth bump" at the crossover.  You can either eq it out, ot just cascade two 6dB HPFs and two 6dB LPFs to create a Linkwitz-Riley crossover at 400Hz, which will sum flat.

5) You'll also need to set your output format to a higher number of channels; you'll probably want something like "5.1 in a 7.1 channel container"; if you do go that route, you'll want to use RR or RL for mixing instead of U1.

mwil,
Thanks.  Understood and good points.
On 3., I believe the internal crossover netwrok on the Revel F208 will sort out frequencies above 270 correctly.
5., Would you mind explaining why I need 5.1 in 7.1?
Right now this is just an experiment.  I feel like I am giving away some amp power and piston power by setting a standard x/o of 80 Hz.
I have measured with REW the 2x2 8" woofers of the Revels flat down to 35 in my room.
Thanks again

[mwillems]

5., Would you mind explaining why I need 5.1 in 7.1?

Because the output format module is first and cannot be moved subsequent DSP modules only have the channels available in output format to work with.  So if you have 5.1 in output format, the channels above six will not be addressable or usable in subsequent DSP modules.  They'll look like they're there, but nothing you copy to them will actually get copied.  I.e. they won't work (IME).  That's precisely why the "x channels in a y channel container" options exist.  In "5.1 in a 7.1 container" 5.1 is the mixing target and 7.1 is the total number of channels available.  Channels 7 and 8 will just be empty, which is exactly what you need.