Hi Larry,
Here's a thread that explains what to do.
... how to set up OmniSynth for General MidiScroll down to a post from Jim111, he explains it.
It sounds quite a bit more complicated that it actually turns out to be.
Essentially, if you navigate to
C:\Program Files\IK Multimedia\Instruments\OmniSynth 2, you'll find a folder called "GM Prog Chng Bank". This folder contains the midi maps for general midi. Jim suggests copying these to x:\bb as it makes them easier to find because one of the maps needs to be loaded each time BIAB is started.
To load a map ...
1. Click on the VSTi button. (If you cannot see this displayed, click on the
>> to the right of the yellow cross to view icons that are not on the menu bar.)

2. Click on "Load Default Synth" (1); the dropdown sythn menu (2); select SampleTank (3).

3. When SampleTank loads, click on "Program CH" (1) and then select "Open Map" (2).

4. Now navigate to the map files at
C:\Program Files\IK Multimedia\Instruments\OmniSynth 2 and select either one of the STMP files. (It's definitely easier to fine the files if they are copied to x:\bb.)

That's it.
Open one of the midi-only styles in BIAB and double-check that SampleTank is indeed now operating as a GM synth.
All the best,
Noel