Cox in Phoenix uses 579 MHz downstream for a DOC 2.0 modem. Two filters are used in the system, a blue filter that gives standard basic and HSI and a green filter for HSI only. The HSI line should be a direct line to the CE Box and is usually connected to the main drop with a 2-way splitter, HSI off one side, the video off the other. Keep in mind if you use a house amp (2-way or 4-way) you will increase your return by 4 or 8db because of the internal splitter.
This is CABL.com posting #306629. Tiny Link: cabl.co/mbrVN