First my comments on plenums are in regards to running them correctly, as Jaubert intended and not the other dozen different ways aquarists have tried, some with success but most failing.
Second if dsb does not work, have a look at the coral growth in Nigel,s FTOTM and Quinn,s tank in the journal forum.
Both of these aquarists have run dsb,s for some time. I cant speak for them but both have told me its part of their success.
Point being, they all work if done correct and properly maintained for that particular type of system.