I'm in complete agreement with Nick. If you are at all concerned with good sound, get some stands.

The problem you're going to get placing your Danes in your wall unit is the rear port isn't going to have enough room to breath. At moderate to high levels, you'll likely encounter "chuffing" and other nastiness as the air tries to find a place to go. This is exacly why your trusted dealer told you a they need a minimum of 18". If Dyn supplies plugs, you're going to need to use them if you insist on bookshelf placement. The downside is a noticeable reduction in dynamic range. Considering your speakers, that kind of untapped potential is somewhat like have a Ferrari with gears 3 thru 6 locked out. What fun is that?

Sorry Howard, but you and/or your dealer should have considered this before you purchased rear ported speakers. Unless you can return them, I'd start looking for stands.

Good luck.