The key appears to be the configuration of your pre/pro (Cinema 11). If you can make it work such that the LFE and line outs for the L+R are separate it might be doable with the MiniDSP.
I'm thinking along similar line with the Marantz NR-1504 which has line outs for the L+R. In DIRECT/PURE DIRECT mode, there is no base management by the AVR and the full range signal goes to the L+R power terminals as well as the pre-outs. As the speakers are satellites with the F3 at 90Hz, need to fill in the lower octaves via a sub.
Got the Rythmik F12G. It's got an LFE input as well as a pair or RCA L+R inputs with phase, PEQ and roll off switches. The sub's RCA L+R input is ignored when there's a signal to the LFE - so this works out for me. The thinking is of running a pair or RCA cables from the AVR to the F12G and adjust the settings to see how well it can be integrated in DIRECT/PURE DIRECT mode.
Not sure if the above idea will help you, but something to consider if your subs support it.
Maranatz NR1504, Oppo BPD-93, MTV 7000D, LG LW6500, aTV, WDTV Live, Harmony 650 remote, KEF E301, MiniDSP(2x4), Rythmik F12G