The question: our current water softener has a clack style bypass valve with matching fittings attached to the plumbing via PVC. What's the best way to replace these fittings and other parts of the connection if I'm installing a different style of water softener?

The longer backstory: It looks like its time to replace the water softener that's been in the house since before we moved in. We had a plumbing company out today to evaluate why it was acting up and they advised that the softener company is out of business and servicing it wouldn't be worth the cost because it's probably at least 10+ years old. They advised replacing it and gave some quotes. Really great company but the cost is going to be difficult to fit into our current budget (the minimum quote was 3.2k with options going up to 7.3k) so exploring other options by getting other quotes. But I'm also evaluating replacing myself with just a cheaper big box store unit. I know the quality does not stack up to the equipment the company would install, but the price is also 1/5th what I was quoted and the install looks simple EXCEPT for figuring out what to do about these fittings - I can tell those units would need different connections. I have replaced toilets, hose bibs, and faucets of all kinds and am generally comfortable with quick plumbing projects, but I also know there's a lot I don't know so just trying to get an idea for what's involved before I decide which path to take. 

Replacing fittings for water softener connection?