In Nashville start near the Ryman Auditorium.. A lot of pricey bar with live music.. Keep in mind that they are selling booze not music. Tootsies Orchid Lounge has webpage with a webcam.. Keith Urban and Steven Tyler have been in there jamming. Some bands not so great but you might catch a celebrity or two out rubbing elbow with the public. A peek at their web cam would give you an idea of what is happening walking the pub crawl
Here is a link where you might find what's happening the dates you plan to be there.
http://www.visitmusiccity.com/music/livemusic
Hope this helps you out.