Who is your provider? They will usually dictate what customer provided modems are supported on their network. Generally speaking, Motorola Surfboard modems are highly regarded. Take a look at the SB6121 or SB6141 models. There's a new model that came out recently that will support like 16 downstream and 8 upstream channels for when the cable internet providers switch over to DOCSIS 3.1 or whatever the new standard is.

SBG6580 can probably be put into bridge mode then you can use your Apple Airport router to handle all firewall/DHCP/portforward/etc roles.