Bridging Amps for Subwoofers

Make that "halve". Thank you. :)

Bridging does not half the current. Read a recent thread entitled BIAMPING under Speakers.

I think it is important to use a high current amp that easily doubles into 4 ohm loads. Most subs have pretty nasty low impedance characteristics. I doubt that the manufacturer recommends 400 watts @ 8 ohms. Since you are not using the amp in a "full range" application, you do not need to spend big bucks so long as it has sufficient current and handles the impedance dips.

The manufacturer suggests 400 watts.
Out of the many great ones, who would you recommend?

Bridging adds power but cuts the current by half. Usually makes things worse. I would recommend a new amp. The good news is that there are many great woofer amps around for not a lot of money. How much power do you need?