Jim, I wish you'd have recorded that living room session. from your discription, it sounds like a really fun thing to hear.
And I have no problems with pushing musical boundaries, but from a more traditional perspective I'd say translating old time fiddle tunes to the mandolin is a little more natural than translating them to the tuba or midi sampler. First off, you've got the strings tuned to the same notes so that slides, drones, and double stops are reminiscent of one another. More importantly, mandolin does have a presence in old time music--even if it is a small one. So, when I hear a mandolin, it seems to fit in a string band context. A tuba would be about as incongruous as a mandolin in a marching band.