Thanks for the replies.
I have a coax out on my digital cable box(SA Explorer 2000). I use this to get DD on the 38 premium channels ( only Showtime ch. 240 is 5.1, but the others and the ppv channels all sound better in DD ). I have a Toshiba SD-2109 DVD that has only coax digital out. I guess my worries are covered for $130. Do any of you use the 4 coax and 4 opto in to one coax and one opto out device? Or do any of you know any more about it?