Purchased a meshwifi6 system

Can be. Router or AP mode. AP mode maybe perfferred since you have a router already. 

A couple thing. 

• which mesh system did you get? There's a lot of wifi 6 (AX) systems
• what AC2600 router do you have? AC2600 is a speed and not a model

You have options. 

1. you can just replace it and use the mesh system

2. you can connect the mesh system to the AC2600. If you do that, put the mesh system in access point mode to prevent a double nat. Also, make sure the wifi channels used between the 2 systems are seperated so they don't cause interference with each other. This lets you use the AC2600 for devices that are close, for IoT devices, or even just as a backup wifi

3. you could hardwire in the ac2600 to the mesh system or one of its satellites (in access point mode) to provide additional coverage if you needed it. Say if you have a satellite at the peripheral and wanted to run an ethernet cord off it 50ft to a garage and put the ac2600 there. (or something like that)

You have plenty of options.