Low end is fine but if u want DTS-HD and Dolby True HD supported, do not get GPUs that are too outdated? As a guide the following GPUs are fine
GT 430 Nvidia and later
HD 5450 AMD and later
FM1 socket APU AMD and later
LGA 1156 socket with IGP Intel and later
Eg : I have a 2008 AMD HD 3200 IGP based HTPC in one of my TV Rooms but in my case i am using floor standers and the lack of DTS-HD/Dolby True HD support is fine with me ^^