I would suggest you take Hikari to Shin Kobe, one after Shin Osaka to change as there is only one platform at Shin Kobe (some Hikari goes on to Okayama)
If you're on a Hikari that has a stop at ShinKobe from Tokyo, then its final destination of that train is Okayama, I would change at Okayama, it is also a crossplatform change there.