I can help ya here. I have the 600a4, two channels running my components, the other two channels bridged to one sub. I will assume you want to bridge your amp from 4 channels to 2 channels.

Since you have 2 subwoofers, each one being 4 ohms, you should bridge the front channels (left & right) together and put one sub on it, then bridge the rear channels (left & right) together to power the second sub. You will NOT connect the two subs together; they are run independently of each other.

In this configuration, you will put a 4 ohm load on each bridged pair of channels, which is FINE.

Hope this helps.