Actually, audio has a way to set the analog input range: it has input
gain control (multichannel, yet) as part of the mixer interface.
Hm, I looked at that, but I don't quite see how it's flexible enough. For
example, the MAX197 (the A/D chip that is of interest to me) can be set
to go from 0 to 5V, 0 to 10V, -5 to 5V, or -10 to 10V. The "gain" knob on
the mixer is an unsigned char. I could set some "magic" gain values to
make that work, but it just feels ... wrong. And there's not a good way
to query capabilies using that interface, from what I can see.