I have'nt done an install for years but from memory I think you will need
A power cap
A 3 way power lead splitter each with it's own individual fuse and 3 positive leads from the 3 fuses to the 3 amps.
Either 3 way splitter (or 3 separate) for the earth and 3 extra earth leads to the 3 amps
Phono leads depend on how many phono outputs you have behind stereo and what your running each amp for (i.e treble, bass).
3 way splitter for remote cable.
But again this all depends on what your running and what each amp is going to be used for.