Pc has only spdif and have to recheck if only 1 usb port so as could be limited in connections if that could be used.
will still be the same thing,
USB is digital
to get the best from your surround you really need an analogue output,
otherwise just go for cheapest option of one of those spdif to analogue cards
or,
do you have a headphone out.?
only my opinion mind, but I had this same thing with my cheapo surround sound, found the quality was better just using the phono out to phono in on my surround, than using the spdif to analogue converter,
I actually use it now combined with an ARC soundbar, and it sounds really good,
when watching the bike raciong I can hear the bikes coming from behind me and across the livingroom,
the soundbar just adds that bit of ooomph to it,
music wise, the sound bar works better, with the sub of the surround kicking in when needed