So from what I can find online:
- Import Melody from MIDI file from Synth V
- Enter the key, tempo and chords manually
- Select a style and generate the music
I'm guessing BIAB is not intelligent enough to match the generated music with the imported melody MIDI file? The 2 will just sound awful?
If the melody has some form of accompaniment, such as a bass line together with some other instruments, then BIAB can work out the appropriate chords. If the melody only consists of single notes, any matching chords could be interpreted in many different ways. Even an accomplished musician / song writer could determine multiple different chord sequences, none of which may be correct.
It's not related to 'intelligence', it's related to having adequate material to work from.
I doubt anything would sound 'awful', it may just not sound right. I'm guessing that you are not very experienced with music, especially music theory.
What does your Synth V Melody consist of?