Thanks much for the replies, Optodata and JL_JL. This problem turns out to be a different one than what I reported. This is now SEMI-SOLVED, sorta, at least IDENTIFIED:
After producing the video in question I first tested it on my tablet. The sound imbalance I described was very pronounced - weak voice, loud music and FX. Now I've streamed it to my TV for testing - same problem.
But doesn't that sound familiar? Google gives you lots of results on the topic of people struggling with weak voice/loud music and FX when playing movies on their TVs. They hold their remote, constantly turning volume up and down. Well, that's mostly a problem with 5.1 surround soundtracks being played on stereo systems. Various "solutions" are posted, including throwing sound to one side so it plays back in mono. If people have a full home theatre set up, they can change the balance so the middle speaker with dialogue is louder.
This can also be an issue even when 5.1 isn't involved. There are various "enhancers" which do aural tricks to boost the width of stereo and/or tweak the EQ in various ways. So another piece of advice I found online was to turn all those things off so you have a better chance of hearing the soundtrack as it was originally produced.
I've noticed before that my PD produced videos will sound wrong played on a TV, but it's more pronounced in this particular project. My soundtracks are almost always complex, lots of layers - AND, Optodata, it's rare for me to use the raw sound on a video clip. I do all my sound production in other sound programs and then import the tracks. The relative balance between the tracks is then done in PD. This project has a produced vocal track, separate sound clips of my original music, separate FX tracks etc.
Also, JL_JL, thanks for the tip. I checked, and I do have Stereo selected in my Preferences.
This project, as usual, sounds fine on the computer. It's exactly as I want - not only with the project playing in PD, but the produced file also sounds exactly the same in Windows Media Player, VLC, any player. It's all good. It's only on TVs and devices where there can be a problem.
If you guys aren't hearing a sound imbalance when you play produced projects on a TV or tablet - I don't have any idea why my results are different.
I'll just tell people the recommended way to watch this is on a computer - and if they watch on TV, which of course would be preferred, I'll ask them to try tweaking their sound settings.
One more note - This issue is still frustrating. If I lowered the sound while editing to levels that work on TV, it could probably be 6 DBs lower - way too low on the computer - and how would I accurately know how low is low enough without numerous, tedious rendering tests?
Thanks again. I may try tweaking a few places in this project where the imbalance is most pronounced, but I can't re-do the whole thing. Not sure what I'll try on my next long project. --