From the UA-5 user manual, located in the handy dandy archival info area of this site:
Advanced mode
The UA-5 will operate in this mode when the rear panel Mode select switch is
turned ON. The special driver included on the UA-5 Driver CD-ROM will be used,
allowing audio to be recorded/played/edited with high quality and stable timing.
In Advanced mode, audio signals can be transferred between the UA-5 and the
computer at a resolution of 24 bits and sampling frequencies of 44.1/48/96 kHz.
Select this mode if you are using an application that allows high-quality audio
recording/playback/editing, such as an application that supports 24 bit audio
(e.g., the Cakewalk series or Cool Edit) or an ASIO-compatible application (e.g.,
Cubase VST, Logic Audio, or SingerSongWriter).
Standard driver mode
The UA-5 will operate in this mode when the rear panel Mode select switch is
turned OFF. The standard USB audio driver included with Windows will be used.
In standard driver mode, audio signals are transferred between the UA-5 and the
computer at a resolution of 16 bits and sampling frequencies of 44.1/48 kHz.
Select this mode if you are using an application that uses Window’s own
functionality, such as an application that uses the computer’s CD-ROM drive to
play back CD-audio, or an application that uses the software synthesizer included
with Windows.
The standard driver that is included with Windows does not support ASIO.