I'm eyeing the 6 CD blues/rock piano set by David Cohen on sale this week. I already own the 4 DVD blues piano set. I'm wondering if the CD set has enough material different from the DVD's to be worthwhile? I know there's a 7 day refund period, but my schedule is too busy right now to have a chance to listen to the CD's right away. Should I jump on this sale, or skip it? Thanks for any advice!