I did ask this question to PAD sometime ago about their cables and what they replied was that apart from no difference in the looks, the Rev A was more hifi sounding while the Rev B was more musical and correct sounding! Apart from this, the Rev B is more extended than the Rev A especially in the upper regions and to a certain extent the lower regions! As such, if you have both side by side, you might feel that the Rev B is slightly more brighter while the Rev A slightly more warmer sounding but actually it is just revealing more! I've compared both the Colossus ic's and I find both give the details but I slightly prefer the Rev A as I find it a bit more warmer! Hope this helps!