I guess that since the 726Vs are within a couple hundred dollars of the 816Vs, I will probably opt for the 816Vs.
Actually if I had never listened to some older recordings (it was actually some Led Zeppelin), then I probably would not have noticed the high end brightness. When I first listened to them, it was with some modern jazz and R&B recordings and they sounded so smooth on those that I was leaning towards the 716Vs. As an example of what I was hearing, on the Zepp recordings, with the 716Vs I heard more snare than head impact when the snare drum was struck and the cymbals were quite harsh. after about 15 minutes, I felt that I was approaching fatigue. With the same songs on the 816Vs, you could definitely hear more head impact as the drum was struck and the cymbals weren't as shrill and overall was much smoother. I have listened to some of my vinyl Zepp recordings and the recording is kind of bright anyway, but I do listen to a significant amount of stuff from that era.
I don't what the model numbers were, but they were hooked up to all Arcam equipment. From what I have heard, their electronics are not considered bright, which, if true, indicates that the brightness was coming from the speakers.
Both models have the same tweeter, so I'm guessing that the difference in sound come from the cabinet design and perhaps a different crossover.