I don't think a network filesystem is going to give you enough state information to do this quite as simply as you asked. One solution would be this:
On the server side, run a script that looks for your 'successful' string as you described. When it finds the string, have it write a new file into the shared directory.
On the remote side, run a script that checks for this new file, e.g.:
test -f newfilename && echo 'Success!' && rm newfilename
Once you've been notified, you can delete this new file and loop around for the next time. The file creation and deletes should be reliably communicated across the network.
In terms of hardware, according to Mactracker, Mac Minis (and most other Macs) since early 2006 come with a 3.5-mm analog/optical combo jack and models since mid 2010 also come with an HDMI port, both of which should support multichannel audio if your source material provides it. You can find the specs for your own Mac by clicking the "This Mac" item in the left-hand pane.
Specs for the current (Mid 2011) Mac Mini say:
HDMI port supports multichannel audio output
and for most of the other models, as an alternative to the 3.5-mm analog/optical combo jack, this Apple support page says that you can also use a mini Display port to HDMI adapter to receive multichannel audio and video (though I'm not sure what software support for this would be like):
These computers supply multichannel audio (up to 8 channels) and video
signals over Mini DisplayPort:
MacBook (Mid 2010) and later
MacBook Air (Late 2010) and later
MacBook Pro (Mid 2010) and later
Mac mini (Mid 2010) and later
iMac (Late 2009) and later
Mac Pro (Mid 2010)
To connect your television or other
HDMI devices to your Mac, use select third-party Mini DisplayPort to
HDMI adapters that conform to the VESA v1.1a DisplayPort
Interoperability Guidelines
Depending on the software player, it should be just a question of connecting the HDMI/optical output to your recevier and getting multichannel output. I use XBMC and get 5.1 surround sound output (AC3 or DTS) over HDMI, and I believe the latest "Eden" release supports 7.1. It also does blu-ray (rips only, I assume), DVD and has an excellent plug-in system which includes Netflix. Alternatively, Plex is an another alternative and will do much the same thing. Once you get your media set up, both will work pretty much out-of-the-box.
As for a TV tuner, Elgato's EyeTV looks very good.
Best Answer
You could fashion a service in Automator using the Terminal.app and your shell with something like: