External Display only 1080i, 720p or 1600 x 900 Resolutions

Ever since I believe OS X Lion, everytime I connect a device for an external monitor I only have specific resolutions. I work in broadcast and I use Black Magic Design products such as ATEM Switcher and DVI to SDI Extender yet the only resolutions I can output to it are 1080, 720 and 1600 x 900. The devices on older OS X systems give the following resolutions for which is what the ATEM Switcher is made to input for:

HDMI Input Resolutions for Computers

720 x 480i 59.94Hz, 720 x 576i 50Hz, 1280 x 720 59.94Hz, 1280 x 720 50Hz, 1920 x 1080 50Hz, 1920 x 1080 59.94Hz, 3840 x 2160 23.98Hz, 3840 x 2160 24Hz, 3840 x 2160 25Hz, 3840 x 2160 29.97Hz. Note: Also supported are; 24, 30 and 60 Hz inputs when switcher is in 23.98, 29.97 and 59.94 Hz formats respectively.

But on Mavericks I can't output at specific resolutions like standard definition which is a real problem because I have to use hardware converters to take a 1080 signal down to standard definition which is very annoying and means I need to buy more equipment.

Is there a way I can get more options when extending my desktop to get more resolutions because this is a real problem for us.