First of all you need to be a bit more specific. There are several models of Firestudios. They have different specs and I/O options. Which are you using? If you are using a Firestudio Project then the answer is NO as it does not have ADAT I/O. And you can NOT daisy chain via firewire interfaces from different manufacturers.If f, however, you are using a Firestudio 26x26 you may be able to use the Saffire as a standalone AD/DA converter. This then would be a question for the Focusrite forums. But I know the Saffire Pro 40 can be setup for standalone:
https://support.focusrite.com/hc/en-gb/articles/206849939-How-do-I-set-up-my-Saffire-or-Scarlett-1st-Gen-for-Standalone-Mode-Again tho....if you are running a Firestudio Project, (rather than a 26x26), the ONLY way to expand it is to daisy chain it with ANOTHER Firestudio Project. That will give you eight more channels. You can however, get two more channels from your Saffire by connecting it's SPDIF ports to the Firestudio's SPDIF ports. But, again, if you are running a Firestudio Project there is NO way
possible to get 16 channels by using these two devices together.
That being said we can help you better now and in the future with a bit more info......if you will post your system specs in your signature, (see my sig), we will be better able to troubleshoot your problems. Without knowing what type of pc you're running, what OS you're using, what DAW etc....we often can't recommend a "simple fix"
If you have not already done so please READ THE MANUAL!