I remember seeing a tv programme were "an expert" said that Bluegrass only works when amplified. Clearly, he is referring to the fact that the banjo - in particular - would throw out the balance of the band if the sound couldn't be modified by amplification.
I haven't read much of the above but I'd like to hear a combination of frailing banjo, cello and voice. Now I'm pretty sure that would work beautifully in a purely acoustic - non-amplified - situation.
Talking of cellos, has a cello ever been featured in the Transatlantic Sessions tv series?