Dear Pinky Makus,
I pronounce it
"iss TH muss"
"iss" = "Bliss"; Criss"; "Diss"; "Hiss"; "Kiss"; "Miss"; "Swiss"; "This".
"TH" = "THaw"; "THor"; "THigh"; "THink"; "Thank"; "THanks"; "THursday";"THesis"; "THousand"; "THeatre"; "THeft"; "THeme"; "THeory"; "THick"; "THief"; "THin"; "THree"; "THirty"; "THrill"; "THroat"; "THrob"; etc.
"muss" = "us"; "bus"; "cuss"; "fuss"; "Gus"; "muss"; "puss"; "plus"; Russ"; "suss".
However, my Oxford Dictionary of English, (2006) gives:
1) "iss TH muss"
2) "ist muss"
3) "iss muss"
"Take your pick", as they say where I live, (when they offer you a Rock Bun to eat!)
I hope that this helps.
Les