It would be a helpful starting point for you to differentiate among the various options on A/V equipment.

http://en.wikipedia.org/wiki/Surround_sound
http://en.wikipedia.org/wiki/DTS-HD_Master_Audio
http://en.wikipedia.org/wiki/Dolby_TrueHD

Pro Logic can sound wonderful compared to typical stereo sound from TV speakers, but it's no substitute for the real deal (digital discrete, DD5.1 and higher), which does not sound as 'hollow' as Pro Logic. Compare what you hear via Pro Logic with DTS-HD or Dolby True HD and you get a better sense of what is possible by employing a newer A/V receiver, better speakers and a blu ray device.

hth,
Pedro

p.s. although it's more complicated, I'd still encourage you to let your cable box & receiver handle the audio instead of optical out from the TV. You'll generally do better this way.