Is it possible to change the resolution out of game, I am unable to change the resolution in game to the native resolution of my monitor (2560X1600) without encountering the following error.
"DirectX Error: DDERR_INVALIDOBJECT"

I'm also unable to change my resolution to any that are x32 bpp, I'm only able to cycle through some x16 bpp ones.

That 16 is hard coded. It doesn't actually pay any attention to the bitiness of the screen mode you're looking at. You'll get 32 bit whatever you select.

As for the resolution, I'm not sure. I have a vague memory that directx 6 didn't allow maximum resolutions that were above 2048 in either direction, in which case it would be a dx6 limitation and not anything to do with omicron, but I can't double check that right now. I might be thinking of an earlier version. :/

Yes you can change resolution outside the game.

Go into your Start Menu and then under GOG and Omnikron there is a link to start the game and also one called Settings, use settings to select your resolution.

It opens in a small window and you can select graphics driver and resolution from 2 separate dropdown menus

Well thanks to Iain I'm one step step closer, however most resolution choices in the settings don't stick, and the game defaults back to 1440x900 no matter what I set it to, the only resolutions I can change in the settings dropdown that stick are any resolutions that are smaller then 1440 wide.

Any resolution set higher then 1440 wide in or out of game does not stay and always will default back to 1440. Also being able to look at the list of available resolutions, it seems the only one listed that won't work is my native resolution of 2560x1600. Which may lend some credence to what timeslip said.

So unless not doing something I'm supposed to (beside confirming the resolution change when I make it) Then I'm pretty much stuck having to change the resolution 18-21 times every time I start the game.

1440*900 is an odd default, and a particularly brutal one IMO as it is 16:10 and won't play nicely with my 16:9 screen, to say nothing about my reluctance to game below my LCD's native res (Anachronox was a tough exception).

While I regret that I cannot offer assistance to your troubles (and I'd better not start lest I start coveting that WQHD+ screen lol) I would like to thank you for bringing these resolution issues to light so that I might avoid a purchase that I'd grow frustrated with. I'd love to play this, the last time I saw it was on the Dreamcast, but not if I can't get it to my ideal res.

Its true that it is a pain to re-change my resolution each time I load the game, but I wouldn't let such an issue dissuade you from this game, I also cannot speak for others if this is even a wide spread issue or if I may just have drawn the short stick in this scenario. If this was the only issue you used to chose not to purchase the game on I urge you to reconsider.

Also remember I stated that 1440x900 was the default, however the out of game changes to that resolution would hold (for me) if I chose a smaller width first.

I ran into this resolution problem also. And there doesn't seem to be an external config to start up.
However I did find a workaround that works well enough for me.
In the menu I changed the resolution from 1440x900 to the lowest 640x480 saved the settings, restarted the game and than changed to 1280x720 and saved. From now on the game remembered these settings.
It's not 1920x1080, but looks good enough and is at the right aspect ratio.
The added bonus is that the font is big enough to read unlike at 1920x1080.

If someone finds a way to keeps this at 1920x1080 with a readable font I'd like to hear it.

I would love a sequal, too bad quantic dream keeps teasing at one for years, then nothing.

You seem to be right.
Could you check this fix?