I think I've got my first problem fixed (about the devices).  But now
I find that xmms is perfectly happy with my sound files, but mpg123 is
not.

It just gives me all kinds of unpleasant messages like:

mpg123:  Can't rewind stream by 984 bits!  [zillions of these, with
various numbers substituted for 984]
and 
big_values too large!
and finally
Blocktype == 0 and window-switching == 1 not allowed.

Any clues about what's going wrong?

thx,
R