I don't remember if the PS2 plays dvd's or not, but I know the Phillips DVD player does. I believe that will also do Dolby DTS 5.1 out over TOSLINK or digital coaxial. The TiVo can make sound, but there's nothing like THX or DTS on a nice sound system.. Without that, you just got volume...
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the ps2 can play DVDs, and will do so over optical toslink iirc. My wii and my cablebox both have digital audio out, iirc as well
Cable box probably has TOSLINK, but not DA, from what I can remember about them. Even my sat will only do TOSLINK, unfortunantly.
DA is a dead technology unfortunantly. PS3 does HDMI/TOSLINK as well. (and 1080p... Yum.)