Acoustic Strawbs. I'm going to see them Saturday night in Atlanta. There is a DVD of the Toronto show and a CD as well. You might also want to check out Gordon Giltrap. Good stuff.
Buckethead has some great acoustic/progressive stuff. Try "Electric Tears" or Population Overdrive". Do a search at Amazon & read some reviews. It's instrumental.
Return to Forever had a few acoustic cuts. No Mystery had a few and the earlier ones were mostly acoustic, although Chick would break out the distorted Rhodes on them too.
Most of the acoustic "prog" that I know of is more jazz than rock though.
Early Zawinul was acoustic, but not terribly fusiony at that point yet.
You could try the Hancock/Corea dueling piano recordings "An Evening with Herbie Hancock & Chic Corea"
From what I have read and heard, there is very little acoustic stuff. Lots of it is more jazz than anything else. I have not heard the Strawbs, but I will give it a check. I would love something by King Crimson, Dream Theater, maybe acoustic Pink Floyd/Roger Waters, etc. I wonder why this hasn't been tapped.
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