What many people have done is to use a HDMI splitter(one in - two out) like one of these: http://www.monoprice.com/products/se...=hdmi+splitter
Don't use a passive version.
That will allow the HDMI to feed through the Pioneer like you currently have as well as to the soundbar. You may need to use two remotes.
Alternately, you might try connecting the cable box to the soundbar via HDMI and then out of the soundbar to the TV via HDMI. Then use an optical cable between the cable box and the Pioneer.