Distortion/Clipping when exporting 24bit/48khz AIFs

So I'm working on a project in which I was asked to send 24bit/48khz AIF files. That's a first for me. Normally I'm asking for 16bit/48khz or 16bit/44.1khz, and usually WAV, although AIF doesn't really make a difference.
 
Anyway, If I export 16bit/48khz AIF it sounds perfect. 24bit/48khz AIF sounds like lots of clipping/distortion gets introduced. I've tried a variety of the subformat options but none of them seem to fix it.
 
Any ideas on what can be causing this? I'm using a ton of VST instruments and effects, prochannel, all kinds of stuff, but again, a 16bit export sounds 100% perfect. It's the changing to 24bit that ruins it.
 
Thanks!

spitballing, could it be defaulting to your hardware outs when you change format in the export preferences? Somehow bypassing your mix bus?

OK so for now problem averted... They said 16bit/48khz is fine. But out of curiosity, if I want to avoid this issue in the future... I'd imagine the real solution next time I know someone is going to need these settings is to start a project at 24bit/48khz (or whatever is needed) to begin with and start from there so that I'm mixing from that point... what settings do I want to change exactly to get that result? 
 
I know where to find under Preferences / Driver Settings to set 48khz as the default, but what about the bit depth? Would that be under Preferences / Audio Data where I have the Record Bit Depth and Render Bit Depth? It seems the default is 16bit and 32bit... Should I change Render Bit Depth to 24bit? Or Both?
 
Thanks