Do you really need a "bottom feeder"? I'd expect the SAPs and the Giant Danios to scour the whole tank when you add food.
How about a riverine dwarf cichlid pair? My new Steatocranus tinanti duo (too young to say if they are bonded) are such a contrast to my other riverine Steatocranus casuarius, in that the tinantis are always out and about despite being the smallest fish in my Rio240 by a country mile (4-5cm, although they should eventually reach 10-15cm). Just like your SAPs and Giant Danios, they love a strong current (8-15x true water turnover) and if my pair are anything to go by, they will love exploring the heavily furnished ~2/3 of the tank floor (excluding one open long side of the tank in the strong current) that you need to provide for the SAPs to prevent "pacing" (sign of boredom).
Other possibles that spring to mind are...
Ancistrus (BN catfish), will love the current, you could add the "lemon" variety often missold as L144 if you wanted some colour
Synoodntis flavitaeniata (Pyjama Syno), lovely marking, at the social/gentle end of the syno scale (although my four often have minor battle wound scars!)
I'd love to say Synodontis brichardi, a bit for territorial/fiesty but doable as singletons or 3+ groups, but I'd be concerned about their caudal fin without seeing interaction first hand
Chaetostoma milesi?
Glyptothorax spp?