Older XTR cranks - replace or adapt?
The shifters+front derailleur don't care about the type of chain rings you're using (just that they're sized appropriately and you're running a double/triple as you were before).

On the one hand, the adapter you linked is about 75 dollars + the cost of regular rings (which should work fine). On the other hand, replacing the crankset means a new bottom bracket (octalink v1 isn't exactly popular anymore,but its not hard to find replacement octalink v1 bottom brackets) and a new crankset. 

I'd probably personally opt for the new crankset and BB, since I don't know about the reliability of these adapters and the price difference is pretty small (maybe 15 dollars). Plus, then, you don't risk someone putting a Octalink v2 BB on there some point and then ruining the crank.