Well, almost three months later I've been able to obtain both a V1 and a V3 (MP and LP) K501 and was able to compare both of them. For the record, the "problem" with the V1 K501 I have was that the recabler did indeed flip a phase on a channel, which is what caused it sound so funky. The two versions are very similar in terms of tone and quality. The main discernable difference is in the midbass - the V1 is lean and tight throughout its entire range, whereas the V3 has a slight midbass hump, which can get just a teensy-eensie bit sloppy on fast, bass-heavy songs. Besides that I don't have the time (or the ears, or the propensity) to discern more differences between the two. I'd be quite happy with either if I had to pick one over the other, but I don't know which one I prefer. Oh well.