ok tried 2 things:

1. used compose to first merge 'chest' and 'abdomen' objects and the 'joined vertices', then saved new obj file, loaded into poser.... however now crashes every time when I try to run the simulation :(

2. tried assigning the 'trim' to soft_decorated group... surprise... surprise it worked!! :) ... I didn't expect it to work at all, but it looks perfect! (hope this works with other more intricate clothing as well) great tip and easy solution! Thanks.