I’m sorry, but do you mean the Railcraft Loader/Unloader can’t handle inputs to a large crucible? I use a 3x3 track and if you load blocks of dust you can fill the entire crucible at once.
You can also put Mass Storage on the sides of the Loader and it will pull from those, not just the internal inventory. I’ve run 10k Hematite dust through a large crucible in a long batch before.