"...I don't really know of a good way to test/isolate a worn CV other than to drive the car in circles (hard left and right) and listen for clicking...."

That's a good test especially if you accelerate (apply torque to the axles) while turning tightly. It might also help to have a passenger in the RH seat to get their opinion as to which side they think is doing it. Then swap seating positions and do it again. Then take a vote. Then flip a coin ;-)

I'm currently trying to find a good axle rebuilder as our 2005 S80 with 150,000 miles is starting to do the same thing. Also there is a whole bunch of slop in the LH axle that makes a "clack" noise when shift from reverse to drive or vice versa. (No, it's not the axle bolt.) The boots on that car are still good and tight also. I prefer to have the original GKN axles rebuilt rather than throw some cheap Chinese crap in there. In the past I used Axles Unlimited but the last I talked to them they said they were having trouble getting the right parts. Raxles told me they couldn't do Volvo axles either. I'm not looking for someone that just repacks them and puts new boots on. I want someone that has the right machining equipment to grind the channels at the correct arc, etc. I see on Youtube where some guys just grind them out with a hand-held die grinder - no thanks!!