I have the "advanced" driver installed, but I've still switched the ADV to "off" and recorded 16bit a few times without problems on an XP machine.
The ADV on/off controlls the a/d converter, so if you have it set to "on", it will send 24bit to all digital outputs. This means if you have a digi-mod UA5, you'll be sending 24bit to the USB, coax & optical. I'm not sure what it means if you have a stock UA5 - I would think any software monitoring would be at the same bitrate you are recording at. If you connect a 16bit device (JB3, MD, DAT) to the 24bit output, they will truncate to 16bit. I've done this with a DAT as a safety net in case my USB recording to the laptop had issues.