The real question is what resolutions really work on his monitor. If 1680x1050 doesn't then I wouldn't call that abnormal..
I don't know what resolutions are avaliable in the graphics settings, the highest any monitor that I have available to me is 1280x1024. Therefore that's the highest I use. I don't know what Miri uses it's a good bit higher, but he does use Nvidia cards.
You can manually set your resolution by opening the Admiral.PRF with Notepad or some other Text Editor(which only exists after you have altered either a Sound or Graphic setting in the ingame menus).
Line 5 the 4th and 5th numbers are the resolution. In the example below it's set to 1280x1024 resolution as that is what I have set it to.
2
0 3 1 1 1 0 0 1 0.25 1 1 0 4 1
7 15 15 12 32 1 1
None
0.75 5 3 1280 1024 0 1 0.625 4 0
1 0 0 0 0 0 0 0 0 0 0 0
You can set resolutions that are NOT selectable by manually entering them there or even enter resolutions that Are selectable manually if you care to. If you screw the file up and Legacy fails to open or work properly just Delete the file and that will revert Legacy to the Defaults and you can go back in and change a setting ingame to recreate the file and start over.
That's the best help I can be with the limited info available..
Consider this your 'Pad' to discuss the 'Game' on a 'Daily' basis.