Watch the Week 3: Sliding 9th Riffs online guitar lesson by Bob Wolfman from Essential Guide To Jazz Blues Comping
I've included a couple of examples of some common usages of these forms. I recommend you listen to the horn section in B.B. King's band Roomful of Blues, Gary Moore's horn section, or Larry Carlton's Sapphire Blue to get some more ideas on ways to use these chord forms. You can slide all of the tones for the 9th forms or just the top 3 notes. Horn sections either play notes in unison, or they can play chords where each horn plays a different chord tone. The latter scenario is most often how a horn section will play in a blues band, playing a repetitive "riff" with this same sliding effect, back and forth using the same chord voicing. Whether you play it on the guitar or use a horn section, this is an indigenous stylistic technique in the blues. For the 9th chords, some players use the 5th in the bass, which adds a little different feel and "color", but it's subjective as to when and what you use. One of the coolest things to do with sliding 9ths is to incorporate a riff or repetitive bass line, then it all gets tied together...sliding chord form with a riff. This technique is a mainstay for Chicago blues, so just listen to Muddy Waters or Buddy Guy. This is really what Chicago blues is all about.