The issue was that I was running version 2.1 of AMD's SDK which wasn't seeing my 6800 card. I installed version 2.4 and all 3 cards are working now.
I'm running Ubuntu and attempting to get my 3 cards up and running. All 3 cards show up in aticonfig and also with lspci commands, but when attempting to launch phoenix with the 3rd GPU it says it can't find the device and only lists 2 of the 3 GPUs. I've looked through the forum and none of the posts found so far seem to provide a solution to my problem in particular. Any ideas?
* 0. 01:00.0 AMD Radeon HD 6800 Series
1. 06:00.0 ATI Radeon HD 5800 Series
2. 07:00.0 ATI Radeon HD 5800 Series
* - Default adapter
lspci | grep VGA
01:00.0 VGA compatible controller: ATI Technologies Inc Barts XT [ATI Radeon HD 6800 Series]
06:00.0 VGA compatible controller: ATI Technologies Inc Radeon HD 5800 Series (Cypress LE)
07:00.0 VGA compatible controller: ATI Technologies Inc Radeon HD 5800 Series (Cypress LE)
No device specified or device not found, use DEVICE=ID to specify one of the following
- AMD Sempron(tm) 140 Processor  Cypress