Considering both of these amps for my set-up. Know they may not be the best out there, but they fit into my budget and are both putting out 100 watts x 2 at 4 ohms, which is exactly what I'm looking for. The 401s is around $20 more expensive than the 400s and the only difference I can see is the low/high pass frequency on the 400 is 50 hz - 210 hz and the 401 is 50 hz - 250 hz. I'm not really up to speed on all the technical specs, so I'm not sure if a 40 hz difference is worth an extra $20? The amp would be used to run a Focal 165 K2 component set.