The 4004 can be bridged. It is not recommended, but it is entirely possible.
Downside is that the higher rail voltage compared to a Palladium will make it more likely to over-power the output transistors and damage the amp.
The 8008 series amps cannot be bridged according to Klipsch due to output instability. (I'm not sure how using an external bridging adapter would cause instability.)
Audio by VanAlstyne sells a bridging adapter, but for what it costs, you might as well buy a different amp.
http://www.avahifi.com/index.php?option=com_content&view=article&id=115&Itemid=238&74a0ad6b5f7a1df0ef4ab98b8fffbb41=9c2db362af96dc17562cd401d4ab6657