New Samsung UN55KU6500 is connected via ARC HDMI to the 975 on both machines.Netflix, Amazon, etc, streaming from the Samsung. Fabulous sound. However, if I increase volume there is a gap in the sound. While watching tv, the word unlock is displayed and no sound heard for a couple of seconds. Separately, can't control volume via the Samsung remote.

Look through the Samsung manual. It sounds like the TV has some feature which may need to be turned on or adjusted for HDMI ARC use. I don't use ARC so I am making some assumptions as to how it is used but...I don't think you will be able to control volume unless the 975 is involved. Program your Samsung remote to control the 975 and see if that helps.

Yea, I would expect the volume on the ARC to be fixed, just like if you were using an optical out. You'll be expected to use the 975 for volume control. If you're actually changing the ARC output level, or if the TV temporarily de-syncs the ARC output when you attempt to change volume on the Samsung, the audio dropout you're hearing on the 975 is because it's re-establishing the HDMI link.

I have tried unplug and plug both machines to no avail. Samsung has a system setting to enable Anynet which is what they call ARC. ARC allows both machines to talk to each other. This is how the 975 is receiving the sound and it is great. I cannot find any reference to an ARC system setting on the 975. There is a "punch through volume" feature, though that seems unrelated.

I have a second smaller setup with another Samsung and a Vizio Soundbar and subwoofer and it works beautifully. Sound not as good, but not terribly bad either.

I am changing volume with the 975 remote and every time I do, there is a silent gap. Same when I change channels. This didn't happen with my old Pioneer VX.

There must be something I'm missing.

Meridian self powered center, right and left speakers plus Meridian 2x10 subwoofer. Surround left and right Polk Audio.

Look at pages 31-33 in the 975 manual.

In the 975 Input Setup menu page, for your ARC input, make sure you set the Video selection to none (----), with the audio setting selected as HDMI-ARC.