The K-1000s are my favorite headphone. I prefer them to all the top tier phones including the R10s, Qualias and HE-90s (haven't heard the LCD-2 yet). They are the closest thing to an uncolored stethoscope to the recording and system for better or worse. So, you should hear the K-1000s with a proper amp before making any hasty decisions.
Like swt61, I feel they cover all music well if they do it for you. However, if the O2s bring you to bliss instead and you're looking for something as a secondary or different flavor, why not sell the K1ks+amp and go for the R10s. Don't bother with the Qualias unless you have tough ears IMO. Bliss + R10 is not the worst way to live.