Are you sure it is only 8 by 8? Most fireplaces have larger flues.
Use a 6" round to 7" oval appliance adapter and run oval into the first tile, usually 4-5 feet.
The oval will get you past the damper with ease.
Damper sealing kits make that part easy also, just glue and screw.http://www.chimneylinerdepot.com/index.asp
This link is broken, either the page no longer exists or there is some other issue like a typo.