In Reason you can "downsample" to 16bits while bouncing or exporting (You're asked to set audio file parameters before processing...).
There's no project bit depth setting in preferences - only sample rate (that switch both the project and the soundcard setting).
You may set the project bit depth in preferences in Logic and in Live, but not in Reason.
I don't find it as any kind of disadvantage. And the magic is that you can use in your project audio samples (loops..) of different bit depth and sample rate.
Just for the record: update your soundcard's MixControl and firmware. There were some issues with firmware in earlier versions as I recall. I use my Saffire Pro40 with 3 different Macs and different OS - Leopard, Snow Leopard and Lion and make 8 track live recordings all the time.
It works now perfect in all of them - no issues at all.
Greetings from Stockholm.
"Reason has always existed, but not always in a reasonable form" - Karl Marx