I'm not sure about 4650 but this is what i tried on XOC 4890. It has 2 DVI connector.
1)I use 2x ATI DVI.HDMI connector.
2)I use 2 LCD monitor using HDMI link for audio and video.
3) Each LCD monitor is configured as 1080P. One main(Disp-1) the 2nd as extension(Disp-2). I can run applications such as games, progamming, HD-TV, Blue-Ray on any of the display. I drag it with the mouse.
4) The sound defaults to my primary video Disp-1. If Disp-1 is off the sound goes to Disp-2. Take note this is the audio through the HDMI connection. If you check or open the Catalyst control center (CCC) the display designated as HDMI will have the audio sound. Somehow the software limits the audio to only one DVI/HDMI output. Take note that both connectors are fitted with DVI/HDMI connector.
I just got the additional DVI/HDMI connector from ATI. I will call tech support againt pertaining to how the software select which output to allow the audio to come out.