You want to know the sonic differences between the I and the III. Unless some one here has actually owned both you may have to rely on a mixing of the reviews on Soundstage (I believe) and 6moons. I like Potis' comments on 6moons. I bought the Bolero's and found his review of them, right after he reviewed the III's, to be very fair in its description. I have no reason to believe that his review of the III's would be far from the mark. From what he said, I would be cautious in matching them to a Mac 275 unless you know in advance that the tone would be to your liking. From what I have heard, the original Sonata, and its successor the II's had a warmer tone with somewhat lower resolution than the III's.
FWIW.
FWIW.