I'm running into an issue that deals with loading more then 16 instruments into Sibelius 7.  Everything in functioning correctly, but if I add another VDL instrument past the 16 mark, or try using an instrument change, Kontakt is replacing a previously loaded instrument and playing back a random sound for the previous voice.

I know how to load sounds into slots 17 - 64 in Kontakt, but I'm not sure how to get Sibelius to recognize and sync the to those slots and playback correctly. 

Sorry, here is what I'm using:

Sibelius 7
VDL 2.5.2
Kontakt 2
Mac Book Pro

When working with Kontakt as a plugin, it's unfortunately not possible to load more than 16 instruments per plugin instance, whether it be in Sibelius, Finale, Logic, Protools, Cubase, etc.

The solution to your problem of running out of instrument slots is to load another instance of Kontakt to your Active Devices in Playback Devices, in much the same way you did when first setting up your Playback Configuration. If you have a healthy amount of RAM, it wouldn't hurt to just start your project with 3 or 4 instances so you can just set it and forget it, not having to worry about whether or not you have enough free instrument slots.

Exactly.

Those other page buttons in Kontakt (17-32, 33-48, 49-64) are only useable if you're working with Kontakt in standalone mode. Most likely, it'll be more convenient to just load two or three separate instances of Kontakt Player in Sibelius's playback configuration and call it good.