Option 1: If you really like the Dali Ikon 6's, get them, the Onkyo 606, and use the receiver savings to get an inexpensive pair of surround speakers, and second-hand sub. Use this setup, phantom center channel, until you can get the center channel that matches your 6's. Upgrade your surrounds if you feel you need to. After that add a second sub.
Option 2: For the price of the Dali's, you could get a pretty nice pair of bookshelf speakers, matching center, and a sub. Then do the rest of Option 1, but you'll have a center & better sub.
Option 3: Do all of Option 2, then get a pair of the Ikon 6's, and move your bookshelves to the back.