You can connect and use a router with your HT2000W modem, and pretty much any router will work. A lot of people choose to use their own router's WiFi instead of the HT2000W's built in WiFi.
However, if the same band is used at the same time from both units, they may interfere with each other somewhat. If you find this to be the case, you can disable one band in the HT2000W and the other in the add on router. This way, each device is utilizing a different band. e.g. use the 2.4GHz band with the HT2000W and the 5GHz band with the router, or vice versa.