I've been experimenting a bit more and managed to create a macro in Notepad++ which works mostly, although I don't think it's necessary. The XML export seems to import fine into BIAB but needs some tinkering because SMP itself is creating the problem.
Within SMP I found two main problems. The bar doesn't always start in the correct place. You can correct this by dragging the bar start line. The other problem is NC. This isn't recognised in BIAB so it causes the beats / bars to offset.
A minute of tweaking from within SMP should create a musicxml file that imports well into BIAB.