We did get the B-W but in just the SM, starting in mid-'72. '73 was SM only in the US so there wouldn't have been much chance to get the B-W DS over here. Citroen thought they would get a bumper height exemption for the SM in '74 but didn't so some American spec SMs were sent to Japan of all places. It's sad that they didn't get the exemption as SM production fell from 2619 cars in '73 to 294 cars in '74. Having US sales wouldn't have made up all that difference but probably would have amounted to several hundred cars - in France the introduction of speed limits due to the energy crises just killed the SM. I have driven a B-W SM and found that the gearbox really hurts performance, plus they weren't very long lived so it's just as well that they're rare outside of the US - four speed Citromatic would have been much more pleasant and reliable though I prefer the five speed manual. '73s got the 3 liter version of the C-114 (same as the Maserati Merak) which helped the B-W a little. Contrary to what a lot of European sources note, there were both 2.7 automatics and 3.0 manuals, although both are rare. The 3 liter C-114 was never injected for any car, with Maserati sticking with the tried and true triple Webers to the end of C-114 production when they killed off the Merak in '82. Ironically, Maserati wasa very early adopter of injection back in the '60s when they used the Lucas mechanical system on late 3500s, Sebrings, and Mistrals. I think the reversion to Webers may have been related to Weber having a large emissions lab to help customers meet various international standards. Bosch did as well, but what with Weber being Italian it was no doubt easier and cheaper for Maserati to work with them and so the D-Jetronic system used on the C-114 died with the SM in '75 after the final 115 cars were built.
As far as the XM goes, the same guys who brought over a small number of CXs tried to bring in the XM as well, but after six cars gave up as the cost to convert it to US spec was too much. I've driven one of the six very briefly as low speed, would love to have been able to spend more time with it!