Not only do the eagles have great guitar, they also have great harmony vocals.
I have used Band in a box, but it works different from a midi editor program. In Band in a box, you enter the chords in their respective place then you choose a style and it creates music from the chords you have given it. So if you entered C-F-C-G, the program could play that progression in the style that you chose say country, blues, swing ect.. It sort've builds a song from the chart you give it.
Creating your midi files is a lot of work, since you have to play on a keyboard all the different parts, even the guitar parts. That's why if you listen to a midi file the guitar parts are somewhat cheesy since it's very hard to duplicate the strumming on a keyboard. Works for me since I remove those tracks. Basically I don't bother trying to program songs myself, I just download them somewhere. One of the secrets of midi is to have a good sound module or sound card, usually the sound cards which come with a PC are poor quality compared to pro audio stuff, especially at high volume.
However you seem to be intriged by progressions, Band in a box would give you a quick reference of how these would sound if a band were to play them. It's pretty good actually and relatively easy to use.
For live music, I'm much more comfortable playing bass, I just don't have enough live experience on guitar yet, however I've been practicing quite a bit. Also practicing vocals.