By standard to connect to the cloud you can do this in one of 3 methods:
* 3CX SBC.
* Remote STUN/direct SIP via RPS
* VPN
Unfortunately the Cisco's by default would not support the SBC or STUN (this would be for preferred phone models only).
Your models are not supported at all and thus do not have a template in 3CX. Your only option (unless you want to write yourself a template) is a VPN connection or SBC and manually pointing the phones to the SBC address as the SIP Registrar.
Dependent on the amount of phones you have I would say that this is a lot of hard work and you need to weigh up configuration time vs getting a nice cost effective "supported" alternative.
Despite what some might say personally I find the Cisco phones a real pain to work with in regards to setting them up with anything that isn't a Cisco UC product - as that is what they are designed to do by default.