What cable for Line level audio to outbuilding?

["longwood" <BillShopping@xxxxxxxxx>]

I want to run a line level audio line to an outbuilding that will have
its own amp and system.  (we currently have speaker on the back deck
and we want the ability to have the same music playing).  The run will
be a total of 175 feet, with about 100 feet underground.  The options I
see are

1)  a shielded 16/2 or 18/2 wire.  Problem is I can't find any that is
rated for exterior use and even in a conduit I am sure it would get
wet.  I used this wire well in the past for interior use.
http://www.generalcable.com/NR/rdonlyres/879E734E-36FB-4997-8D19-8AF9A8B24090/0/Pg99_MltiCondShldRiser.pdf

2)  Two rg6 coax cables with rca connectors on the ends.

3)  A cat5 solution with baluns

Any recommendations or input as to the best way to do it as well as
sources for the cable would be appreciated.