The biggest audio delay is when starting playback on Plex video content, especially after rewinding or forwarding. It takes 2-3 seconds for audio to kick in.
I don't listen to music with the TV on. Regardless of the source (Roon, Spotify or Tidal) then the first second of any track from a "cold" start is missing. If I skip to the next track in the playlist it's a smooth transition, but stopping the current track and selecting another one will then miss the first second.
I actually do have an Arc Genesis run that I'm comfortable with and haven't felt the need to send to the guy from AVSforum to tweak. It was the fan noise and the other quirks of the Anthem that compelled me to order the A1H earlier tonight.
My plan tomorrow is to listen again to a few more demo scenes on the Anthem, then swap the 6500 back in to see if my memory is over-valuing the performance of the 6500. Maybe I think "oh boy actually the Anthem IS better".
The A1H should arrive Tuesday and then I have 30 days to decide whether to keep it. (Although if the Anthem sells on Ebay then that will make the decision for me)
As has been said many times, if you are comparing two AVRs, even if you level match them to within 0.1 dB, and in pure direct mode, you will still hear a difference and form an opinion if you do it
sighted. This is found in also many forum talks from people who had done those comparison. Yet, if done in double blind or even single blind, people could not hear such differences. So I think if you really think you can hear a difference then go with the one who felt sounding better, if not then I would say keep the Denon and sell the Anthem. There are many Anthem fans so it should be easy to sell. With ARC G though, as I mentioned before, don't expect flat and smooth bass response, depending on your room/speakers, the best you can achieve is probably within +/- 3 to 5 dB, that's isn't bad at all. With my D&M before, I could achieve +/- 1 to 2 dB, but audibly speaking it is hard to tell a difference. However, with ARC G, if you don't check it with REW, you could be listening to more than +/- 5 dB in the bass range and how good that would sound relative to the 6500 would all depend on your own preference, and we all have different preference/taste. So you may want to also compare in pure direct mode, Anthem does not have that mode, but you can disable ARC G as you must know that already.
As for delays, I believe that's simply due to the design of Anthem AVRs/AVPs. My AVM has delays even when playing the test tones, it varies from less than a second to a couple seconds (between channels) when playing the tones. Coming from Denon/Marantz, I was hard to accept in the beginning, but I got used to it, not really an issue for me anymore.
The A1H will not sound better (okay now I am lowering your expectations, not intentionally...), but if you look at the innards, the block diagrams, and Denon's own measurements, you will see that this thing should beat most if not all so called integrated amps in the same price range. That thing ideally should be used as an AVR, or use a 2/3 channel amps for the LCR and use the remaining amps for the surround and height channels, otherwise may as well buy an AVP and it won't cost you much more.