As far as the 7960s go, they're a whole different beast than the 7970. The configuration file syntax is arguably easier, and they don't have the 7970's habit of going into a reboot death spiral when there are XML parsing problems on the configuration file. They also work flawlessly with Asterisk.
So at the moment I have five extensions on my Asterisk box with a single SIP gateway. I'm going to be dropping in a Linksys SPA-3102 to act as both an FXS and FXO analog adapter for a regular POTS line, and run through the dialplans on both that and the Asterisk box to bring at least one POTS line into the mix, along with an analog phone. If that goes well, the other lines will get the same treatment. The SPA-3101 seems to have the right featureset, including internal dialplans to shift calls from the analog phones to Asterisk first, then the connected POTS line should the Asterisk server be unavailable. Also, in the event of power loss to the SPA-3101, it will fail open, providing the analog phone with a passthrough to the POTS service. Hopefully, it will arrive early next week.
In a perfect world, I'll have everything running through Asterisk with several POTS lines and at least one SIP trunk, a smart dialplan to prefer certain trunks over others depending on the number dialed, and failover to POTS. It'll be a little bit of a project, but every step of the way, I'm more impressed with Asterisk and TrixBox.