I agree with Tom about midi tracks, they sound horrible. Incredibly useful for practice but I can't understand why so many players use them in performance, it just takes away from the overall sound. Playing a cappella (I had to look it up) might not suit those wanting to play melody lines and fills, or country songs. But if you need backing surely it sounds a hundred times better to play with any half decent acoustic guitarist. No shortage of those. The surface has barely been scratched as far as other potential duos (duets?) with pedal steel goes.
Jon




