Is there a way to turn on an "audio info" status line in any of the layouts, like this (from DeadBeef) ?

Only very partly for now.
Only the current song's info are available, and you can't format them (other than using pango markup for font, size, bold, color ...)
example by replacing this line in the "Lists, Library & Context" layout :
VBmain      = HBmenu _HPmain Progress
VBmain      = HBmenu _HPmain Progress Text1(markup="channels=$channel|$samprate Hz|$bitrate bps|$filetype|$length")

You can get the attached result.
(you could also add current time with a Time widget)

More things will be possible in the future, but currently this is it