I have had the 840c for 16 weeks now. Burn in took about 4 - 6 weeks, and I play the system at least 6 hours a day. The burn in does not surprise me. Most everything I have owned has not come into it's own until 2 months in or so. I can say for certainty that is due to the electronics, not growing accustomed to the sound. To test your stuff, just play your handful of reference material each time you put in something new. Then listen again after a week, 2 weeks, etc, to the same material and the differences will be apparent.
I also have the new DAC Magic for my second system. That took 2 weeks of 24/7 burn-in to come to life. Now it sound really great driving my PC sound. I notice with that unit that it always needs a few hours of power up to sound it's best.
Sorry to sidetrack. Back to the 840C. It is not bright at all. Very refined sounding. Interconnects will make a difference, but if you are thinking of changing those, wait until after burn in. I use Nordost Blue Heaven RCA which work very well.
BTW, I also use an XLO reference 2 power cord for the unit. The basic power cord that comes with the unit is not very good and does not allow the unit's full capability to come through. In fact, for any that complain of brightness, that might contribute to the issue, depending on what amp, speakers, etc. you use. I have also tried Shunyata Venom I believe it was. That made the sound too smooth which drove me nuts. Tried another XLO I believe it was, clear coating with silver insides. That sounded terrible, but then it sounded terrible no matter what device it was connected to. It was also the most expensive. Cost does not always equal quality.
Lastly, after picking up some Nordost Flatline bi-wire speaker cable, the 840C sounds even better, along with the rest of the system.
I don't have any fancy equipment, with the 840C being my most expensive purchase. Using a NADT753 for both stereo and surround, with B&W 603 S3 as the mains. Plus a lot of tweaks, such as Richard Gray and PS Audio Quintet's, and decent cable all around. Those that have heard the system are very surprised at how clean and refined sounding the system is. I'v listened to much more expensive 2 channel amps, and speakers that are double the cost of mine, and did not sound near as good. Proper room setup, cables, and clean power make a lot of difference.
