Thank you, I think a sump loaded with live rock and chaeto would provide most of the benefit as far as pods, micro fauna activity, nutrient export ability ect. And I would certainly recommend making the change.
I have found with sump type refugiums though accessibility can be an issue (I wedged a 40L aquarium into the stand underneath a 125 one time, and working on anything in that sump was a massive pain!).
As far as the DSB specifically, I like it for chemistry reasons: it gives me a noticable 'buffer' for various water conditions (pH, additional reduction in nitrates, some dissolution into trace elements). For a while I had multiple systems and did some experiments with what I called my detatchable DSB (a modified 5 gallon bucket with some of that plastic filter media above a 10 inch or so DSB) the bucket could be moved from system to system, and thus it was easy to observe water conditions with and without the DSB. In systems that had something to reduce nitrates already (my reef which had a bare bottom sump with LR and halimeda) I didnt notice a change, but in other systems (my 60g scorpion tank which had less than an inch of sand in the bottom, no fuge LR and mostly fake decor) there was a difference in nitrates.
Bottom line, I use it because it makes it so that I can be lazier and know that my water parameters are more stable
But I dont think its 'needed' if other things are there to replace its function.
