You could use the Sub XLR output for the rear sub and the RCA SW2 output for the sub in the front. The XLR output will be higher, but you can compensate with the subwoofer's settings.
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AvFan
Outlaw 976 | ATI 2005 | M&K 850s Left, Center & Right, Surround-55s, MX-70B Sub | Harmony 950 remote | Panamax 5100 | OPPO UDP-203 | LG OLED55B7