You can use Polyphone to create an SF2 GM set from the Band-in-a-Box Sounds SFZs.

http://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=411193

http://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=408973

SFZ you can use Keyswitches for Bends, slides etc.. but you can't do that with SF2.

If you use VSTSynthFont (1.096 / 2.096) - VST instrument as the default, that will load any sf2/gig GM or load a different SF2 GM for each track giving you more control over the sound as it's hard to find an SF2 GM that is perfect.

http://www.synthfont.com/soundfonts.html
https://musescore.org/en/node/94941
https://musescore.org/en/node/103046