Probably Light Brahma hen with a Red Silkie rooster would work best.
I don't think you can get sexlinks from the colors you listed in your title (Black Silkie and Buff Brahma).
For sexlinks in general:
Either cross a gold male with a silver female, or cross a non-barred male with a barred female.
Some crosses can be sexed by the chick down color at hatch, others have confusing colors as chicks but can be sorted as they grow their feathers.
For Brahmas and silkies, the possibilities would be:
Silkie hen who is barred, cuckoo, or crele <--> any color of Brahma rooster
Sons will have white bars in their feathers, daughters will not (if you get chicks with large amounts of white, check any black feathers to see if they have white bars on them.)
Brahma hen who is Light or Dark (not Buff or Partridge) <--> silkie rooster that is buff, red, partridge, or any other color that looks some shade of brown
Sons will be grow feathers in white or white + black, daughters will grow feathers that have some shade of brown (usually with some black or some white as well.)