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Sony DAV-F500 system:
Here is what I found about
your current Sony setup,
Even the rear surrounds are not truly wireless — they require connecting to the surround amplifier using conventional speaker cables. The fronts and centre channels connect directly to the subwoofer, so too does the main unit via a control umbilical lead.
Seems to me the slick looking Sony system uses a proprietary connection scheme. Consequently, the speakers and subwoofer will only work with the supplied amplifier+player unit and than too only when connected as specified in the manual. Further, Sony player is not a Blue Ray Disc (BD) capable and if that matters, it is yet another limitation. Unfortunately, the only way to upgrade will be to completely ditch the DAV-F500 and start from scratch. In short, 1x Receiver, 1x BD Player, 1x New set of Speakers and subwoofer.
Here is an
AH System Recommendation article that will get the thought process going. I recommend reading it not for the specific products, and rather for the types of equipment you will need and any questions that come up.
Harman Soundsticks III:
Unless you connect that PC to a very good sound system, like a full blown home theater, it will be tough to discern the improvement in sound card's signal quality. I recommend sticking with the on-board sound card unless there is something like line noise bothering you.