Ok I have a 2007 NBS LTZ Silverado that I added a Tahoe touch screen & with the help of this board I have a rear view camera & voice recognition. Today I drove a 2008 NBS LTZ with stock Nav. & rear DVD. The owners manual talks about Digital Siginal Processing. Both trucks have Bose sound systems, but I believed my DSP didn't work because it was an add on. The 2008 acted the same as mine , is DSP an option that neither truck has or I just don't know how to work? Look on page 3-5 & the next one in the Navigation manual.