I wouldn't be too worried. I think you got a good price, and even though there's a new HE560 on it's way, there will also be a new successor to the HE-6 around the corner which will push down the price of the HE560.
It certainly could be the 8200DQ doesn't have quite enough power for the K612. I think the K612 is so new there aren't a lot of impressions, but the K601 and K501 I had both really required a lot of power. I think the Audio-gd ROC almost required me to max out the volume to get them to a good listening level. Unfortunately, I couldn't find any solid documentation on the 8200DQ's output impedance or output power. I will say it looks like a very aesthetically pleasing...
Unfortunately I can't find a lot of information on the power output of that unit. Are you totally maxing out the volume, or are you just worried that you've turned the volume too high? What is your Audiolab unit hooked up to? The K601 was a surprisingly power hungry amplifier, so I'm not surprised you need to push the volume.
Also on the stock train. I've tried the K701 multiple times, K702 multiple times, Q701 stock and modded, and K702 anniversary. I think the Q701 is the most natural and detailed sounding in stock form, given the right amplification.