for anyone picking up this thread, read this one
https://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=577563#Post577563

you do get a load of sounds free

i've got the GM mode to work in Halion SE and i'm just working out how to use the standalone instruments outside the GM set.

i've also got the synthfont64 to work now i've got the latest version. timbres of heaven is a nice free GM soundfont.

i also followed Peter Gannon's 'no brainer' post and got the TTS1 free

sfrozando also loads individual sound fonts and there are some good free instruments like the Estate Grand Piano LE which i quite like.

totally agree with Mario that GM sounds and free sounds will never match some of the amazing samples available but exploring the free options will give you a better sound than the standard GM sounds you get with BIAB

so now i've got several midi sound sources - all free - and as part of a mix they can sound quite good.