[Coastsider]

Here's another solution:

http://www.sonorastore.com/510.html

This powered device locks the polarity of the multiswitch on the AT-9 (or AU-9) and has four outputs which can be split to provide inputs for two Zinwell WB68's for a total of 16 outputs.

Here's a link to a diagram:

http://www.solidsignal.com/manuals/Sheet_HRPID1422_11.pdf