Interesting, I am using the Ref 6 connected to a Hegel H20 and then to a pair of Harbeth 40.3XD. I believe the H20 has higher than average gain at 32dB. Also the output/input impedance matching of the Ref 6 and H20 appear to be just barely OK with the avg. output of the Ref 6 being ~600 ohms and the input of the H20 being 9.4k ohms, I am using XLR. JA’s measurements set a recommended lower limit of 10k ohms for amplifier matching so maybe this isn’t a very good match.
@agbrace That 32dB amp gain is definitely higher than average, though not unheard of. This is certainly boosting your audible "chime"! In my case I was running Rogue Apollo Dark monoblocks with ~33dB gain. At times it felt like ungodly amounts of gain. Anyways, inline attenuators (say 10dB) placed between preamp and amp can reduce the chime proportionally if you have the gain to spare (you do, between 14dB Ref 6, plus 32dB Hegel) - BUT most ready-made attenuators are RCA, and you have to deal with the old "does this extra connection & resistor reduce sound quality" thing we all torture ourselves with here (in reality, it’s a negligible impact).
That Hegel’s 9.4K input impedance (XLR) is almost shocking. Much lower than I’d expect or want. That said, it’s a marginal mismatch, but not enough to have bearing on the tube chime issue. The Ref 6 is cap coupled, so maaaaybe you start losing some bass power due to the low input impedance, depending on the value of those caps. Which is a shame because the Ref 6’s "proper" bass is amazing.