Question about Netgear R8500 Nighthawk X8, ac4334/n1000

Nothing to do with DSL. The router's "aggregate" option is used to double the speed of the connection with e.g. a NAS (a set of external hard disks connected directly to your network to store music, films or other data and possibly to function as a mail server, web server, surveillance, etc.) equipped with a network adapter. A NAS (a set of external hard disks connected directly to your network to store music, films or other data and possibly to function as a mail server, web server, surveillance server, etc.) also has two LAN ports that can be combined into one. To simplify, instead of exchanging data with the NAS at 1Gb/sec you will have 2 Gb/sec. Two network cables will then connect the router to the NAS. For this to work, you need to do a little configuration in the router software and the NAS software. I hope I haven't been too complicated...