Omein in beginning of Kaddish, after 'shemei rabboh'

There is no doubt one should answer Omen after "Shmei Rabbo". This is brought in the Roke'ach and the Rambam. There is an argument about Omen after Brich Hu, and Minhag Ashkenaz is against it. There also is a question, according to Minhag Sepharad that say "Veyatsmach etc. Meshichei" if Omen should be said after that, (The גרי"ז סולובייציק held that since the Rambam doesn't mention Omen there - even those who say these words shouldn't say Omen), but there is no argument about Omen after "Shemi Rabbo".

Michael FRBSH