the rotary macerator will not macerate anything in the 2nd slot provided! only does the first slot
The second slot is an additive slot, used to macerate iron directly into refined iron dust.
Also the singularity compressor, for me at least, doesn't consume the whole 8 copper bars when crafting a dense copper plate. Only one bar out of the 8 is consumed, although, it does take 8 bars to start.