I was able to bring my old SFF MythBox back to life today with the addition of a Sharp LC-46D64U.
Im typing this with the Sharp running as a monitor to the linux box. The video card is a Radeon X300 (RV370) running xorg's opensource radeon driver, connection between the two is a DVI -> HDMI converter cable. I had considered getting one of the fanless 3450 cards with HDMI out, but it was unnecessary as this card filled the role just fine.
I removed the old monitor specific resolution lines in the xorg.conf, started up X and was pleasantly surprised to see the TV snap to 1080p. Sharp's EDID is spot on, no fuss what so ever. I set the TV to "dot-by-dot" and the background image displayed perfectly. I watched some 720p TV episodes using mplayer. Things were great, I couldnt be happier.
I need to re-vamp my old myth install and bring lirc back up to work with xmms and mplayer again. I'll probably try out the latest kernel in a few.
In summary, the Sharp 46" LC-46d64u works out of the box with the opensource radeon driver at 1920x1080 with no need for custom mode lines and most importantly with no headache involved!
thanks for the help and moral support