After some investigation, I found both PSA and Total are now recommending Total Quartz Ineo 5W-30 ACEA C2 "low SAPS" oil for DW10/DW12 engines (2.0 and 2.2 HDi). You may not see it listed in your 406's handbook as ACEA C2 oil did not exist back then. Low SAPS (sulphated ash, phosphorus and sulphur) oil is designed mainly for the benefit of increasing life of cats, and helping keeping DPFs and EGRs clean. And this stuff in particular claims better fuel economy too.
Some more info here:
http://www.servicing.peugeot.com.au/med ... df583b.pdf (from PSA Australia so listings are a bit sporadic)
http://total-gbr.lubricantadvisor.com/C ... 1.2009.pdf
I put this stuff in my car anyway, got 5 litres for €30 online so pretty reasonably priced (only a few quid more than Quartz 9000). I don't have a DPF but am interested in the other benefits. I have no idea what sort of oil my mechanic was putting in it, but so far the throttle seems a bit more responsive - not sure if it's just because it's fresh oil or better oil. I haven't driven enough yet to determine if there's any difference with fuel economy. I've heard before from some people about being reluctant to put thinner fully-synth oil in older engines but it seems ok so far - no leaks all over the place... yet. And I guess 122k miles isn't exactly high mileage for these engines
I see Total do not recommend it for the XUD.