A Sizzle is a frizzled Silkie, carrying the frizzle gene - since frizzle is incompletely dominant, all birds that carry the gene will be frizzled in appearance.
Silkie is both a breed and the name of a gene. Not sure what you mean by a "smooth sizzle". If you mean a regular Silkie, a bird not carrying the frizzle gene, with silkie feathering, that is actually a different recessive gene called (a little confusingly) silkie. For a bird to appear silkie-feathered, it has to get a copy of the recessive silkie gene from both parents. Silkie birds carry 2 copies of the recessive silkie gene, which causes their feathers to appear more like hair. So mating a Silkie to a non-silkie feathered bird that does not carry a recessive copy of the silkie gene would not produce silkie-feathered birds.
Clear as mud, right?