Is the hum because of you are using an RCA-XLR cable between the Denon and the AHB2? Asking because I'm planning to do the same, but I probably won't be able to deal with such problems like you.
Since the Meitner has no 12V trigger out, the Denon must be turned on all the time while you're listening to music?
I'm also hesitating to use an AVR (especially the ones not measured yet, like the new Pio/Integra) for music. Even if the measurements on paper are good enough, I just find too many reviews and information on how much different a DAC can make. Now I am literally chasing rainbows, how to make these Kefs sound at least close to how they sounded in the shop, so for stereo I'm now looking for a DAC/pre-amp combo to pair with the NCx500. But frankly, the more I read and research the harder it becomes to make the right decision.
(The following is a bit ooc.)
I just copy/paste a piece from a review of the previous generation of the Kef Reference 3 that I found, about DAC pairing:
"It was natural trying a bunch of D/A converters and Reference 3 actually helped me a lot when I was evaluating such devices.
What struck me first is that these highly detailed and transparent sounding loudspeakers were sounding less impressive, bi-dimensional and almost flat, carrying little to no emotions with entry to mid-level converters. Digital creatures that had dedicated line-amplifier circuits sounded considerably better to those that used over-simplified digital attenuation techniques. For example…I wasn’t very impressed by entry level Topping, SMSL and Gustard DACs that were almost clinical sounding when I was pairing them with power amplifiers. After adding a preamplifier in the chain like Musician Monoceros or Benchmark HPA4, I felt their presence immediately, improving the pace, rhythm and timing and boosting dynamics to higher levels. When I’ve used several D/A converters that had proper line-amplifier circuits, things improved drastically. No wonder Gold Note DS-10 Plus powered by its complimentary PSU-10 EVO power supply, together with the Matrix Audio Element X sounded the best to me, completely bypassing the need of a dedicated preamplifier."
If this is true, I'd have to spend the same money as my speakers cost to get a decent enough DAC for these speakers to sound as intended.
For example, I have no clue which DACs use dedicated line-amplifier circuits instead of "over-simplified digital attenuation techniques" and why would it make an audible difference but I definitely don't want "less impressive, bi-dimensional and almost flat, carrying little to no emotions" - whatever that means. Also, why is "clinical sounding" a problem? I prefer measurements and rather trust the experts on this forum, but there is a strong overlap with personal impressions too and it's hard to separate the two.
Why would a 200 Euro Topping E50 sound any different than a Mola Mola?