he means the tweeters are a little bit louder than the mids, I'd assume it's not ear shattering as he did not descdribe it as "harsh." tried my NAD 304 on Infinity FS speakers before, tweeters weren't a problem if you sit farther away from the speakers. bass response could be a problem though, the "hard" bass naturally loses impactbut the decline in volume was sharper and didn't help the imaging. then again, the 304 isn't exactly known for pounding midbass, although it does reach well into sub-range bass.
what amp are you planning to use? make sure yours has a beefy power supply, the 304 had a lot of reserve but it couldn't keep up with the 3-way FS speakers. curiously enough it did better with my lower sensitivity diamond 8.4's, and that's in my condo with no acoustic treatment.most likely it was the tweeter to mid balance.