The G74Sx provides an optical Toslink signal out from the headphone jack. it requires a 3.5mm plug adapter such as the one
sold here. They also sell ready-made cables with a 3.5mm plug on one end and a standard optical connector on the other. Just make sure your cables are long enough.
It's also possible to run HDMI out to a splitter box with Toslink (optical) conversion. The store linked above also offers these boxes for quite a bit more than a simple 3.5mm plug adapter.
Not sure if you'll have to do some tweaking to get proper 5.1 surround out of the laptop's Toslink digital output, but let us know how it turns out and good luck.
G74Sx - BIOS 203