How to activate 2nd modem in my home?

[cablemodem]

Hi Guys,

I have an arris DG1670 modem at home with spectrum internet service. I want to install 2nd modem at home. I bought a premod Motorola surfboard SB6141 and changed the CMAC address to the MAC of arris DG1670 and connected the cable line.

But the online light and DS UD light is NOt on. It does not work.

Please help me activate my 2nd modem at my home.

Thanks a lot