vga switch causing resolution problems

Hi, I recently bought a VGA switch by MayFlash so that i could share my 22" widescreen LG monitor with both my x360 and my mac mini. The problem I have is that when i was running my mac mini directly into the monitor via vga cable (with a built in DVI adaptor) the display was instantly recongnised by my mac and displayed at the correct 1680x1050 resolution. However, now im running it through the switch im having all sorts of res problems, firstly the mac doesnt seem to be able to detect the monitor anymore and i have a massive list of resolutions to choose from none of which go up to 1680x1050. All of the resolutions are unsuitable as they are lower res and crop / stretch the screen image. The manufacturer of the switch claim there should be no loss of signal and i've tried upgrading the vga cables im using to superior quality ones to no avail, any ideas?