Assuming Ryder is not an option:
Out of Neesham, Anderson, CDG and Munro- Lord CDG is by far the better bowler fot test and FC. Its not even close. CDG can nibble a new ball around on line and length and get Safrican wickets if needed to.
Munro is the better bat and the ideal 6 - but he doesn't complement the current bowling attack well in place of Santner's spin and playing both Colin's and a spinner makes for a weaker seam attack. In case you're not aware - Munro started bowling his seamers a lot in all formats esp red ball last season on Hesson's direction. He has even at times been opening the bowling for Auckland.
T Astle seems to have usurped Sodhi just now outside of T20 on bowling alone, but that could change again.
Munro at 6 would permit A Patel, Sodhi, Santner or Astle to play batting lower.
Kuggs is on the selectors radar and a useful bat. But illness in missing the NZA v WI game has let Fergusson get ahead of him in the pecking order. Southee is under pressure here. But CDG retained in place of Southee in a test last year vs Safrica to permit 2 spin options. In the end Boult was unfit for the 2nd test then Boult and Southee were unfit and Henry played the 3rd. Southee was vice captain at the time to boot! But how do you drop Wagner?
NZ has a lot of options right now in sorting out batting strength. But CDG averages over 36 with bat and under 26 with ball. He's not an easy guy to drop. And its his bowling that has kept him in the team before his latest run of batting scores.
While all the focus on Santner at 6 - it kinda takes away from Niccolls who has been very very poor at 5, despite a ton in a losing effort vs Safrica where he made hay against their spinner and part time spinners. Tom Bruce is an option here, Watling as a batting specialist or even Munro really wouldn't do worse, or Latham could drop down to 5 and a new opener found. Hopefully better than George Worker.