Steam Box?

I am makeshifting a SteamBox for now using components I already have:

ASRock A55M-HVS AMD Socket FM1 Mainboard (I know it's a bastard now, but I have it already)
AMD A6-3600 2.1-2.4GHz Quad Core (just purchased for $25 on eBay, was A4-3300 )
AMD Radeon HD 6670 1GB GDDR5
2x4GB DDR3 1600
120GB Samsung 840 Evo SSD (boot)
2TB 7200RPM HDD
Windows 7 Home Premium 64-bit + Steam

This will suffice for the time being since most games will be Lego games and some Indie games and Minecraft for my kids. Eventually though I want to go with a more powerful config and was wondering if/what others might have built and any recommendations for best bang for the buck? It will be used primarily for controller based games, and would like to play at 1080p although not necessarily at highest details, and will be using HDMI for my video.

Would also like to stick with an HTPC type horizontal case, but fit full height video cards if at all possible, although there are some pretty powerful half-height cards out there right now. I may just stick with my current case is an HEC (7K09BBA30FNRX) with included 300W HEC PSU (hec-300FN-1rx) if there is a decent half-height card out there. The R7 250 looks like a decent choice. I could probably even stick with my RAM, SSD, and HDD, so basically would need a motherboard, CPU, GPU.

I'd like to go with something relatively low power and quiet.

 

A nice steam machine that doesn't cost an head and an eye imho can be built with either 970 or 960 gtx, asus impact mobo, 8gb ram, a nice ssd and a 500W PSU, complemented with an I5 cpu.

 

I've got a half height GTX 750 and it seems like it does great. Mine is not the TI version, but I don't see it on newegg anymore.

http://www.newegg.com/Product/Produ...cm_re=gigabyte_gtx_750-_-14-125-680-_-Product

I was just playing Batman Arkham City at 5760 x 1080 with it. It was running at 99% and reached a max temp of 79C within 10 minutes. Thats with the stock cooler in a Silverstone ml04b case with i5-3570k at stock voltage. I will test it at 1920 x 1080 now.

Edit: at 1920 x 1080 its running around 60% gpu and tops out at 60C.

 

I tried an FM1 APU build before. Terrible experience. Even with using a video card, the system just seemed so slow. I was even using an SSD for boot and had plenty of RAM. The last APU build that I did was with a Socket AM1 SoC. I went with the Athlon 5350 which was clocked at 2.05GHz, an AMD Radeon HD 7570, 4GB PNY PC3-12800, and a 120GB PNY Optima SSD. The system wasn't too bad, but the lack of dual-channel RAM was a bit of a turn off. I ended up selling the computer to a friend about a month or so ago.

 

I just built a mini ITX system. I think you'd better go with nVidia GPU because of the low power consumption/heat.
If your GPU budget is strictly < $100, you can get a 750 Ti for that price.
Otherwise I'd recommend GTX 960 ($199) in case you wanna go 4k. I have it and it runs extremely cool & quiet.