Nigel did you consider VI.One It costs $99 and has 21 Gb of samples. It is not GM it will be more of giving you one plugin per song in BAIB maybe more than one if BAIB and VI.ONE and your computer can handle multiple instances of VI.ONE being used for different parts.

VI.ONE covers every area of sounds: pads, pianos, organs, drums etc. I have but several grand piano including Ivory Grand Piano and I have to say that the VI.ONE "White Grand Piano" sounded very nice as did their "Warm Pad". Some sounds you will find good others not so.

By the way there is a Kontakt based Grand Piano called "Cinematic Samole Piano" that is from Australia and costs only $69 but is supposed to be very good. It is made by the makers of the acclaimed "Cinematic Sample Strings".

Also in late 2019 Korg released the Triton software. It costs $250 and has literally about 4,200 programs and combinations-- of which about 1400 are GM patches. It is a VSTi and hopefully can work OK with BAIB. I am just learning and experimenting. But you get the sounds of all expansion boards plus all the regular presets for a low price.

I hope this helps.