What... there's no big red button? Damn...
*googles firepod*
Where are you gleaning the intelligence that you're working in 16 bit?
I've searched the Firepod manual for you (I'll bill you, OK...) for "16" and pretty much the only time it shows up is in a phone number and at the bottom of page 16. We can probably thus assume it only does 24 bit ...
I'd be looking in Cubase if I were you. I apologise for not being in a position to download 31MB of zipped Cubase 4 manuals for you to pinpoint the exact place, but you can do that yourself, yes?
You have installed the Firepod driver and Cubase is talking to your Firepod isn't it?
There are some regular Cubasers here, one of them will give you more information, I'm sure, once they detect your distress... I've rung the HR Cubase bell for you, but they don't always answer...
Good luck...