I see that GK has renamed the MB2-500 to just MB-500. I assume this is mostly a marketing thing. But some retailers are stating that the MB-500 has been "refined" and "tweaked" over the MB2-500. RMC Audio even states that the EQ is different (but no details). I assume the MB-500 has all the fixes present in the latest (A07?) version of the MB2-500. But what are the concrete differences between the two? I'm curious if its worth paying more for a new MB-500 vs. buying a used MB2-500.