I have not heard the Tannoys but the Dalis are not incoherent. Many of the best speakers available have 3 or 4 different sized cones, domes or ribbons that are integrated into a pleasing whole.
If the Dali distributor has the 400 mkII it should give you an idea of the Dali sound. If you prefer it to the Tannoy, I would consider buying the Dali. If you prefer the sound of the Tannoy Glenair, I would buy that.
Also, the Dali distributor may be able to direct you to someone who owns the Dali Helicon 800 mkII speakers who would be willing to let you listen to them.
If the Dali distributor has the 400 mkII it should give you an idea of the Dali sound. If you prefer it to the Tannoy, I would consider buying the Dali. If you prefer the sound of the Tannoy Glenair, I would buy that.
Also, the Dali distributor may be able to direct you to someone who owns the Dali Helicon 800 mkII speakers who would be willing to let you listen to them.