Hi tgaffor,
I think you have a mistake about the Summetrix architecture. Inside the Symetrix you have directors, boards who controls either channel (SCSI, FC, ESCON, Parallel, Remote Directors), memory boards and disks (disk directors). Each disk director (DA in Symmetrix nomenclature) has 4 SCSI buses, each bus -depending of the symmetrix model- can have up to 16 scsi drives, so the length of the scsi bus (per bus) is not longer than 1 meter (12 feet).. with this length it does not need repeaters internally.
Take a look to the symmetrix 8000 product guide and you will see how is internally.
Cheers.