I am looking at the ways to connect 2 sites with CIX systems ( 670 and 40 ) together so that calls that come in on their analog trunks as well as internal extension calls can easily be passed back and forth.

Sip Trunks?

Strata Net?

Pros / Cons???

Thanks guys!

IP Strata Net is what I'd recommend.

Yep, Strata Net is the easiest route. The only thing you need to ensure is solid VPN connection between the sites.