I am at a loss as to why my '99 V70 rides like an old lumber wagon and need some advice.

At 130K the car was riding beautifully, if a little floaty over high speed dips. Front Michelin MXV's were worn out and had all 4 replaced with the newer series Primacy MXV4's, and it immediately rode quite a bit harder (much harsher impact over tar strips, potholes, etc.)-- confusing, as they're the top-rated tire for ride quality at Tire Rack! OK, shocks/struts need replacing anyway, so I put on Sachs Super Touring as they seem to be the OE replacement. Rode even worse, actually skittering sideways over some RR tracks it used to glide over. Got rid of the Sachs and put on Bilstein TC's which made a slight improvement but not enough. Got rid of the Michelins and put on General Altimax RT43's and made another very slight improvement, but still way too harsh.

The front end was aligned (twice), tires checked, rotated & rebalanced, and when the Sachs were installed I replaced the strut top mount plates & spring seats and the rear shock upper mounts. At this point I'm having to run the pressure low (32f / 28r) to make the ride even tolerable, and both I and our local Volvo specialist are tearing our hair out trying to figure this out. Anyone with any ideas?