Is it possible to turn a computer into a home theater receiver? What equipment is necessary? Does Windows Media Center support this? Can they push out the same wattage?
Of course a modern PC can hndle many functions of a home theater receiver. It has audio I/O interfaces as well as video I/O interfaces. At least at first instance it might make sense to use it this way as well.
At second look you will find that a PC is usually not equipped with a powerful amplifier. What you get from a modern sound card are line-out and pre-amped outputs which require external amplifiers as well as some pure digital outputs. I am personally not aware of any HiFi amplifier which is built into a PC directly. Usually you also want to avoid high-power amplifier circuits within a PC as you would also amplify a lot of noise resulting from power surges and many radiation sources within a PC case. This is also the reason why many high-quality sound cards have a metal shield (e.g. refer to Asus Xonar series). This shield is neither for heat dissipation nor just for "coolness factor"; it is shielding the audio circuits from various radiation in order to minimize their impact on analog audio connections.
So given the fact that you either output digital audio signals (which again need an external receiver or amplifier) or analog outputs which also require an amplifier there is not much functionality of a home theater receiver left which you can move to your PC.
Of course a PC still makes a lot of sense in modern home theater systems - but mainly as an A/V source than as the AV receiver. I personally do not own any A/V source except my PC. My graphics card is connected up to my screens and a beamer, my sound card is connected via S/PDIF to my home cinema receiver which powers a high-quality 5.1 sound system. Using the machine I can turn any 2, 4, 5.1, 7.1... stream into a real-time encoded DolbyDigital/DTS bitstream sent via S/PDIF to my receiver. Well, nowadays you would potentially prefer an HDMI connection, but my equipment is in use since about 10 years now.
Windows Media Center also acts as an A/V source rather than as an A/V receiver. Even though you could use a TV card to get pictures from external sources into your PC and display it in media center. But there is still the problem that you need some external speakers and speaker amplifiers.
Given the prices of A/V receivers it does not make much sense to put these functionality into your PC. The functionality is quite "dumb" and static - so there is no benefit of using a complex software system to emulate this functionality. Getting any Logitech 5.1 system (e.g. the Z-5500 is still a good buy for the money) would probably be a much better choice.
Of course one of the drawbacks of an A/V receiver is that its functionality is static. For example such a receiver would just accept a certain amount of audio formats which it's able to decode. Using a PC as a home theater A/V source also helps to overcome some of these limitations. For example my home theater receiver (Yamaha DSP-A1092) only supports DolbyDigital/AC3 and no DTS. But using my PC I can listen to DTS audio sources while my CPU simply decodes DTS and my Xonar soundcard re-encodes it to DolbyDigital Live 5.1 bitstream again so it's accepted by my receiver. Of course usually this is a stupid thing as you decode, re-encode and decode again which is a loss of quality. But some movies are re-mastered in DTS and the resulting quality is still much better than to listen to the original DolbyDigital bitstream as it is on DVD.
No, a sound card will not provide enough power to connect it directly to loudspeakers.
But a typical A/V receiver does several things: is acts a decoder, to translate things like Dolby Digital to 6 analog signals (for a 5.1 system); it acts as a preamplifier, allowing you to switch between sources and to control volume; and it acts as a power amplifier, to provide enough power to the loudspeakers to drive them properly. The only one of these three that a PC sound card clearly can't do is to act as a power amplifier.
So if all your media was on your HTPC, and you had a power amplifier, I think that's all you need, in principle. But you'd need a sound card with outputs to support all 6 channels in a 5.1 program as analog signals. For instance, the SoundBlaster ZXR card (SoundBlaster ZXR card) provides (analog) FL on an RCA, analog FR on an RCA, RR and FR on a 3.5 mm jack output, and C and Sub outputs on a second 3.5 mm jack. So is seems like you could feed these outputs into a power amplifier and be done, at least in principle.
The release notes for Kodi 16.0 say "Added support for lossless software decode of DTS-HD tracks/streams in videos using libdcadec", so it seems that as of March 2016, there is software to make the scheme described above work.
In summary, the answer to your question is "No, a computer cannot act as a home theater receiver". But a computer plus a power amplifier can do everything a home theater receiver does.
In my system, I recycled a laptop (cracked LCD & lid), connecting it to a 46" LED/LCD TV display, 6OW/ch A/V receiver, & gigabit wired + b/g/n wireless LAN. The old lid, detached & fitted with cushion "feet" serves as a dustcover. I can use its built-in keyboard & touchpad, an external wireless one, or an android app called WinRemote to control it. WinRemote can control Windows Media functions & even duplicate the display on the controlling android device. Certain android phones (HTC & Samsung) can also use built-in IR emitter hardware & a $7 android app called ZappIR to control AV receiver functions. I also use a UHF-to-IR receiver near the AV center with IR-to-UHF transmitters in other rooms to relay IR remote commands to the AV receiver through walls & floors. Great for playing audio or video on CD DVD & BluRay discs in the laptop's internal drive or streaming media from a remote library (Windows 7 homegroup or NAS drive). The receiver I use has multi-zone speaker switching controlled by the remote, too. The receiver is an older Pioneer model (old 480i composite analog video) so I just route the audio from the laptop's headphone jack into the Aux input & audio from the TV into the TV input on the AV receiver.
In short, No because typical surround speakers are energy guzzling buggers, require more power than headphones, power your computer doesn't put out through it audio jacks unless its a specialized motherboard from the future. :P
There are now "SMALL" receivers which connect to your computer via audio jack. This receiver connects usually to 4 simple front and back speakers and 1 sub. while they are small and compact they do cost a crap ton.
Your better off just buying SONOS, there a company that makes wireless speakers just get 2 of those bad boys plug em in connect and your set. They do give a hell of crisp sound and even a little shake if the settings are set up right.
Hope this helps