You need an A/V receiver to make use of the Mirage Nanosat package. You can get one for around 10-15k.
If you get an A/V receiver with HDMI ports, you'll connect the HTPC to the A/V receiver via HDMI cable. Then A/V receiver to TV via HDMI cable again. This will carry both video and audio signals already.
If you get an A/V receiver without HDMI, you'll connect the HTPC to the TV via HDMI. For the audio, you'll use an optical cable to connect the HTPC to the A/V receiver. With this set-up, you won't be able to play the latest DTS-HD and TrueHD sound formats.
If you're going to use this set-up for DVDs only, then you're good with the latter. If you're planning to get a bluray drive for your PC, then I would recommend going for the first option to take advantage of HD audio.
HTH!