Hi Dan, thanks for your input. I discovered further (BIAB 2016) info on this topic. There are (at least) two types of 'rendering' to WAV.

1. BIAB > Menu > Audio > Render to Stereo .WAV file etc...
a. Render to Audio File (dialog) pops up
b. many options are available
c. song is rendered to Song_Rendered.WAV upon clicking
[DXi - Direct Render (save WAV file)]

2. BIAB > Menu > Audio > Render Song to Audio Track (and mute tracks)...
a. no dialog pops up
b. song is immediately rendered to TEMPMAIN.WAV (TEMPMAIN.bt1 also created)
c. lower right 'yellow' message appears alerting to new file location
d. IF Song.MGU is saved in BIAB,
TEMPMAIN.* files are renamed to Song.*,
ELSE the TEMPMAIN.* files are removed

I'd basically given up hope of finding any BIAB documentation (F1, online, etc.) describing the WAV filename subtleties. Then, just before posting this, my mouse hovered over Dialog 1a's [Choose] button, where bubble popup said:

Choose the name for the rendered wave file (*.WAV).
NOTE: The file must reside in the same folder as the
current BB song file. Also, don't give it the same name
as your BB song, since this may conflict with the audio
track wave file.

smile