As far as I can tell, that older Technics can only accomodate a single multi-channel analog (=6 channel, 5+1 ) input. If the Sony you own has multi-channel output you could at least send along Dolby 5.1 and/or DTS to your surrounds/sub. See p.8 of the online user manual to see how a component multi-channel analog output would connect-

http://service.us.panasonic.com/OPERMANPDF/SAAX6.PDF

Since there are no digital optical or digital coaxial (let alone HDMI) inputs, you should probably think about upgrading the receiver so you could enjoy the surround from the Comcast box & also advanced audio codecs of the blu ray content.