Hey Cmalak, checked out the Wilson phase and impedance chart. I was totally floored because it looked very similar to the readings for my Paradigm Signature 8 v2 (w/ Be tweeter). The curves in the bass region look like a double humped camel. Weird/???
www.hometheaterhifi.com/home-theater-speakers/476-a-secrets-speaker-system-review.html?start=3
I don't know if this will be useful to know, but my front end is an ARC Ref-5 and my amp is an ARC VS-115 (w/ KT-120 tubes). Although the Ref 110 sounds better than the VS-115, the two amps share similar power and other electrical attributes and my amp seems to drive my S8 fronts very well across the full FR. I use the 8 Ohm taps; tried the 4 Ohm taps, but the sound sucked. As an FWIW, I recall that ARC uses Wilson speakers in their sound room. So . . . I surmise that you should be getting superb results with your rig.
I would try switching taps as suggested by George (Hifigeek). Also, how old are your Ref 3 tubes. I believe that ARC recommends replacing the 6550C PS tube every 2000 hours and the 6H30 tubes every 4000 hours. If still no luck, call Cal at ARC.
Please let me know how you make out. Hey, at least you can ski on the impedance and phase curves, but only if you're expert skiier. LOL :)