Drok00

I've been historically disappointed with the complete utter lack of features & settings available on ISP supplied equipment. if it does, I would be mightily impressed.

99% sure you would need to switch your additional router it to an AP mode, and plug it into a LAN port, the WAN port would be used if there was an external modem.

You have done liquid cooling setups with your homemade rig, and your more exotic solutions, would you consider trying out something that is more feasible for the average DIY'er? an instant cool water chiller? similar to this unit https://www.freshwatersystems.com/products/oasis-r5-remote-water-chiller-5-gph. it's farily reasonably priced and sized. and if it doesn't work, you can just hook it up in the kitchen! two birds one stone