Is it possible the cable box is defective or has an adjustment to increase its output?

The SA8300HD configures the audio output of the HDMI port ONCE the first time it is hooked up to a device. So if you had it hooked up to your TV then moved it to your Home Theater the HDMI audio output my not be set properly.

Here's a link to the user's manual I pulled that info out of. It also explains how toget in and manually reset the HDMI port.
SA8300 User Manual

Hope this helps...

Thanks, guys, all input is appreciated. Believe me, I've been looking for any settings anywhere in the chain that might help. :-)

The DVR seems fine with the other two processors. It's odd that the output is notably hotter from the 950. My other DVR is dead, but I'll check the replacement when I get it and see if it's the same.

It looks like I have a later cable software version than what's in that manual. There are three settings in the Audio Coding menu: HDMI, Dolby Digital and PCM. When using HDMI for audio, neither of the other settings produces sound. I also tried connecting via coax and setting the coding to Dolby Digital and PCM, but the output level stayed the same.

When you are hearing TV sound, does the 975 report it as Dolby Digital? If so, check to see if the Nite mode on.

There is no reason the cable's DD audio should be any softer than a DVD (well, not during the train crash on Super8). What do you find for volume using DD DVDs?

The 975 does display DD 3/2.1 or 2/0, depending on the signal from the cable box. Night Mode is off.

Let me pop in a DVD here...the only music disc I can find is Alice in Chains Unplugged. (I'm testing with music content as it maintains a more consistent level than dialog.)

Even though it's a quieter acoustic performance, it's still averaging in the low 90s, with peaks around 95-96dB. So it seems pretty equivalent to the Blu-ray output.

If you want to do a definitive test use pink noise with both processors and measure the difference. You can download a test signal from many sources.

I ran the Disney WoW audio test tones with these results. I stopped at 100dB on the other two processors as that was stupid loud for a test tone, and both had lots of headroom left (the 950 volume control goes to +10dB and the 5007 goes to +18dB).

975: -7dB (max volume) = 90dB output
950: -2dB volume control setting = 100dB output
5007: -5dB volume control setting = 100dB output

The 975 result is similar to your earlier test when the MV was at -30. Here, you are able to play an "85 dB" test tone at 90 dB. That's theatrical ref level +5 dB.

The cable box is not defective because it is dutifully passing through the DD bitstream it receives. It cannot modify the levels in a bitstream.

Even though you normally use cable, do you have any OTA signals available? If you can get a network channel from a TV tuner (via S/PDIF) and compare the same channel from the STB, you can verify whether the STB is outputting the "normal" audio loudness or not.

Broadcast TV average audio is modulated much the same as other sources. If it seems to be 20 dB low on peaks, part of that may be due to TV programs having much lower peak-to-average range in the mix. But if you switch to a PPV or HBO movie, the full peaks should be present like on a DVD.

If, in the end, you really want more gain in the 975, give Outlaw a call and see if they have any ideas.

It seems odd the the 975 max volume setting doesn't go to at least 0 db. Most go to at least +10db.

In reading the manual on page 36 it seems that the 975 has some sort of limiter at "0" db where even if you increase the trim the max volume decreases the same amount. Have you tried swapping the HDMI input for the cable box to another and see if it makes a difference.