Hi,
I've only used B2M a couple of times but the .tiff output was 16-bit. There was no option to set the depth so I suppose that's the default. There does not appear to be an export option for Open EXR. Hopefully Allegorithmic will be along shortly to set that straight.
I've been hearing that Alchemist will be superseding B2M at some point - I hope the export options are improved - including non-square output.
Daf