Marantz DV7600 not passing analong multichannel sound

Don't know a better forum to try and find an answer to this, so maybe this is the one...

I bought a Marantz DV7600 universal player a few years back because I like hi-rez multichannel music and have a decent SACD/DVD-A collection. In addition, regular DVD's sounded better to me if I let the Marantz DAC's decode the Dolby 5.1 channel soundtracks and send 6 channel "analog" sound to my Yamaha receiver. For years all was well and good in this world.

Then, suddenly, my Marantz stopped passing sound through the multichannel jacks, although the left and right fronts are still active with what I'm assuming is down-rezzed stereo. The stereo left and right jacks still work as well.

But in the "Settings" menu, the "audio out" choice under the Audio tab (the one that lets you choose between 2-channel and 5.1 channel output) is grayed out and unavailable. The next tab over is "Speakers" and they are all grayed out as well. This happens after I insert a disk and it loads. When the machine is empty or in full "Stop" mode, those options are not grayed out and are available. It's like the very act of loading a disk deactivates the multi-channel out jacks. It doesn't matter what other choices are made in the "Settings" menu. Nothing brings them back.
The digital audio jack still works however. So it still works fine as a normal DVD player with DD5.1 sound, provided you let the receiver decode the audio stream. But no more multichannel music - it just skips over the multichannel or hi-rez stereo tracks on SACD's or DVD-A's now as if they weren't there. It just reads the CD stereo track.

I've tried to contact Marantz for some assistance or advice and they are completely unforthcoming. They absolutely refuse to help or even offer a diagnosis because the unit is out of warranty. Bad additude, IMO; this is likely to be the last Marantz component I buy.

So I thought I'd come here and see if anyone has any ideas about what's causing this and/or how to fix it. Simply unplugging the unit and "resetting" it doesn't help. Thanks to anyone willing to take a shot at this...

Thanks Will. I have tried everything you suggest, all to no avail. There are 2 ways to do a reset (including pulling the AC power) and I've tried them both. My gut reaction is that a chip or circuit board responsible for the multi-channel output has failed in some fashion. My gut also tells me this is an extremely rare occurrence.

Since there's nothing wrong with the laser pick-up or transport mechanisms, the machine works fine when playing ordinary DVD's or CD's. However, that's not what I paid $700 bucks for. I hate the thought of having to buy another machine just to play my SACD's and DVD-A's, especially one with lesser quality DAC's than the Marantz, but if I can't fix this, then I guess that's where I'm going to have to go.

I was hopeful that Marantz engineers, given a complete and accurate description of the problem, would be able to at least point me to a chip or board that might have failed (I can't be the first person in history to have a problem like this, and I'm capable of replacing parts like that), but didn't expect to run into a brick wall of refusal when I asked them for help. It has certainly colored my opinion of that company, and made me reluctant to purchase any more of their products in the future.