Connecting iMac to a second display - what cables?

Hi first post on here!

I bought a second screen a few days ago, the 23" LG M2394D. I have got it connected to my 24" Aluminium iMac. The resolution of the monitor is 1920x1080 and the iMac is 1920x1200. System preferences lets me assign the different resolutions on the different screens, but the quality on the second screen at 1920x1200 is very dodgy. If i put it to 1650x1050 it looks better, but not as good as the apple display. I have also noticed that the picture is 'too big for the screen', i.e. there is some of the picture outside of the screen area that i cant see. I have the screen connected via the Apple MiniDVI to dvi connector and then a DVi to HDMI cable into the screen. Is it the HDMI that is causing some of the problems? would a straight DVI cable work better? Here is the screen: http://www.it247.com/Product/26-M2394D/?channeltype=TFTDisplays&level1cat=Computers&prodid=26-M2394D&level2cat=DesktopsandWorkstations&campaign=ciao&utm_medium=TFTDisplays

Thanks in advance

sorry i meant if i had the second screen at its native res (1920x1080) it looks messed up. If i turn overscan off, then the picture is too small for the screen and it doesnt look great either.