[Avodah] "kesod siach sarfei kodesh"

[Zev Sero via Avodah]

Nusach Sefard, in the introduction to the normal kedusha, says "kenoam
siach sod sarfei kodesh" -- like the pleasantness of the speech of the
holy serafim's conclave.    Nusach Ashkenaz, in the introduction to the
kedusha of musaf, has a similar phrase: "kesod siach sarfei kodesh".
But what does this mean?   Every translation I have seen has rendered it
as if it said "kesiach sod sarfei kodesh", but that's not what it says!
Does anyone know, if "kesod siach" really means "kesiach sod", why they
are reversed?  Or, if that's not what it really means, can anyone explain
what it does mean?


-- 
Zev Sero               I have a right to stand on my own defence, if you
zev at sero.name          intend to commit felony...if a robber meets me in
                        the street and commands me to surrender my purse,
                        I have a right to kill him without asking questions
                                               -- John Adams