The more hrs of burn in I find more and more detail in both sets.. The fx40's tho are kinda unforgiving when using a crappy material but when using great sources they are amazing..they are quickly becoming my favorite set right now. I bought 4 pairs of the 40's just to have as I tend to misplace my sets.
Yes, mine's sounding rich after around 130 hours burn time. Drums and percussion sound wonderful on it, having been listening to one of Jon Durant's albums. It's fast and does reasonably deep sound very well. Eventually, it's gonna be tested head to head with the HA-FX101.