Hi, Tom! This is quite a puzzle you have posed, especially since it's not just you watching. A 5.1 sound system is good because it pulls the speech to the front center speaker. Since speech is the most important part in understanding the plot, it's important that it come through and not be drowned out by music and sound effects. The amplifier can also help adjust the balance, so you could increase the volume of the center channel and decrease the volume of any channels that tend to drown speech. That's a start.
I think that it would be difficult to create a listening environment that works well for both you and your wife with all speakers. Having someone use headphones is the only way to ensure two separate listening environments that won't interfere with each other. What I'm thinking is for you to have a set of headphones that carry just the speech. The speakers in the room could then be adjusted to a "normal" listening mode. Since some of the ambient sound will reach your ears even through headphones, this system still works. Speech from the speakers that reaches your ears will just reinforce the speech you are already getting. Sound effects and music that reach your ears will be dampened by the headphones, but will allow you to hear this part of the audio in a way that won't drown the speech.
So, I would suggest that you hook amp 2 either to the source audio, to a 2nd audio out on amp 1, or to a monitor out on amp 1. Adjust the sound on amp 2 with an equalizer so that it emphasizes the speech and de-emphasizes everything else. Then run headphones for you from amp 2. The speakers will put out a typical listening environment for others, while the speakers + headphones will provide you with a personalized listening environment with the speech having more volume.