Kisame, Kakuzu, Deidara, and even more can't kill 6 paths of Pain? Itachi is basically useless in this fight so he dies instantly, but either way the same outcome still happens. Nagato would be a different story, and Obito solos everyone else including Itachi, Pain and the rest of the Akatsuki if he's included.
Sasori alone would give Itachi a tough time, adding in a distraction like Zetsu clones would consume his chakra rather quickly. Deidara, Kisame, Kakuzu, Hidan and Konon would ultimately defeat Pein. Their main adjective would be allowing Deidara to go undetected to use C0/c4.
itachi and pain would fuss alittle but eventually they will loose simply because of the quality of the rest of the akatsuki members and their NUMBERS. your talking about :
- kisame (the master jinchuriki hunter of the akatsuki who is not far behind itachi in a 1on1).
- kakuzu (very strong and very experienced on the battlefield, with long and short ranged attacks).
- sasori (poison, iron sand and 100 puppets, the man who took on a nation .... do i need to say more).
- deidara (a long range style mad man).
- hidan (hmmmm .... not much but he is immortal and could be used as a distraction).
it would be insane to think all of these characters would loose to TWO shinobi's even if they are very strong. the way i see it, rest of the akatsuki take this mid diff and am being generous here xd puting them against two shinobi's is like saying the rest of the akatsuki members were weak U_U
for real pain and itachi are ridiculously strong and on sage level but the rest are all kage level all those kages together ... its pretty hard to stop if they have good chemistry