This is a way to use the same amps and speakers for stereo listening and surround FL and FR speakers.
By using two passive switch boxes The DirectStream DAC w/Bridge II can be the preamp for the same power amps and speakers used for in a theater system.
The RCA outs of the DirectStream connect to Y cables. One set connects to “In 1” of the first box and out to M700’s. These cables end in 50Hz high pass filters for the 3.6 speakers. The second set of Y cables goes to “In 1” of the second box and out to GR Research W/Frame OB subs.
The XLR outs of a Oppo 205 connects to “In 2” of the first box and out to M700’s. This is a XLR to RCA cable with a capacitor dividing network built into the cable for the 3.6 speakers. The RCA outs of the 205 go to “In 2” of the second box and out to the OB subs.
There is only one stereo out of the first box to the M700 amps. Selecting 1 or 2 does the routing. Same with box to to the OB subs.
Pushing button “1” on both boxes selects DirectStream stereo. Pushing button “2” on both boxes selects Surround.
Very nice ! I am planning to do build something similar myself. But for XLR and with relays instead of physical buttons. And control the relays via NodeMCU and connect that to my home assistant based home automation system as well as IR commands.
I am still in research phase of which relays to go for. I will probably go for point to point wiring instead of a circuit board.
In your experience, did this degrade the sound quality ? And do you hear any pop noises when switching inputs while power amps are on ? Or do you turn power amps off every time before switching ?
Nice! I did exactly the same with 5V relays for automation.
Takamisawa relays, Neutrik RCA, QED/Klotz cables.
Next project will be with XLR. 
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No, the passive boxes have no effect on the signal. My system is very basic with no AVR or Surround Proessor involved.
Amazing stuff ! 
Looks really good and clean! Using ESP8266 inside those ?
Did you use point to point wiring or circuit board?
Do you hear any pop sounds trough speakers while switching the relays ? I am sort of afraid of this because of ground differences of two sources.
Thanks denizpiri! No wifi chip, only 5V relay and point to point wiring (cat7 solid core). 5V coming from low noise HTPC psu when the computer starts and switches the input to AVR. Works really great! In the vol.1 of the DIY input selector, there were pops through speakers because I thought it would be great to switch grounds too, that was a mistake and connected grounds together.
Vol. 1
Vol. 2
In vol. 3 I need to add some Dynamat because the aluminium case amplifies relay click and it’s quite annoying.
