B&W 801 S2 Fatigue VS. 802 S2 No Fatigue?

I recently purchased a pair of beautiful 801M (series 2) that are in near-mint condition. For the past 6 years I've been enjoying a pair of 802 S2. I always wanted the 801's and a pair became available at an incredible price- so I jumped on them. I wanted deeper bass extension in addition to the wonderful soundstage, dynamics, attack, and imaging that I loved about the 802's.

Upon setting them up and listening for a few hours, I was very impressed. Besides the bass extension (although sometimes flabby, depending on the recording), they have a larger soundstage than the 802s. They are also more revealing, which I find interesting because I believe they share the same midrange and tweeter units.

But the more I listen to them, the more shrill they sound. The midrange and treble sound as if an EQ is bumping them by 5-7 dB or so. The resulting glare turns me off after about 10 minutes. I find myself turning the volume down time and time again. This is the opposite of my experience with the 802's. With them, I found myself turning them up without any hint of fatigue, even after hours of listening.

I'm using the same setup with both of them. I have a Threshold S500/II being fed by a Yamaha Aventage HTR (not the best preamp for the system but it sounds very good, at least with the 802's).

Does anyone have any explanation or advice?

I'll be installing a newly purchased Anodyne bass alignment filter tomorrow. The speakers are currently sitting on their factory casters until I can find a used pair of Sound Anchors.I thought about swapping the heads between the 2 models but then thought it may not change anything.

I've done lots of reading here and on other forums and haven't found anyone else that experienced listener fatigue with the 801 S2.