I wanted the sound of Bach. It sung back. I tried bok, still the same. It shows aa but still prounounces like back. If I put a instead of aa in the phonetic still no difference. for aa, it shows spot, hot, sorry as examples but won’t do Bach ( like the composer)
Most native English speaking people butcher the German ch sound (well, in this case the a-ch sound). To balance this out most Germans butcher the English th sound. 
Omnivocal has no concept of pronouncing the German ch or the Dutch g, the Spanish j or g, the Russian kh, …
As for the a sound, maybe uh will help.
Actually I didn’t need the ch sound. I just wanted back to be pronounced with a different accent as the examples show, like box or stop. but nothing worked.
Bach? Back? Box, stop? That is borderlining on blasphemy 