Well,your goal was 1920x1200 85 Hz so at 96 Hz is good no? For resolutions over 1920x1200 better to use downsampling,about the pixel clock if you set 2560x1600 56Hz what happens,black screen? 1920x1200 96 Hz is 322 MHz with CVT,2560x1600 56 Hz is 323 MHz so your limit is between 322 and 323? I don't think that Sunix card has anything to do with that limit,maybe it's only an unfortunate chip of the adapter. About the 120KHz limit,well that is the max horizontal scan rate of the FW900 (121-122 KHz),example you can't do 1600x1000 134 Hz to reach 320 MHz pixel clock because the horizontal frequency is 145 KHz. The card driver are only for USB functionality,about the recognized resolutions the problem is that with these adapters the CRT is seen like a digital monitor,so the system shows you the standard resolutions as they are in the EDID. Example in the EDID there is a 1280x960 75 HZ,in fact if you set that resolution you will see 75 Hz as max refresh rate,i had the same problem with Windows XP which does not support EDID override. You need to use EDID override with CRU utility and set all the standard and detailed resolutions like you want,so you don't have to create all those custom resolutions manually every time you need,but simply you load your saved EDID profile one time.