This can be done, although u still will have a passive network to separate the Mid & Mid bass (2.5 way)
If I misunderstood and u have amplifiers for all separate drivers, then all 6 output channels on the DCX will be used (6 drivers, 6 individually filtered outputs)
If in the future if u do the full 5.1 ...u will need 2 extra DCX.
Why not just build an MTM design ..saves on some outputs, and gains u some db, and u will need only 2 DCX for 5.1