RealTracks are precorded phrases and licks which BIAB picks and chooses to creat a guitar part. if the musician didn't play it, you can get it to play as audio.

However, for what you want to do,midi allows you to play any notes or riffs. If you use a midi keyboard you can play in the riff at a slow speed and create and edit it until you get it right.

Then, what affects the sound is the quality of the synth playing the midi notes. Even on the TTS1 (the GM synth that lots of us use) the guitar sounds are a little unconvincing. You can however buy vst guitars that will sound better. watch the video here to get the main idea
https://www.youtube.com/watch?v=aw5v7JRWUmo