tbh, when running a 4 channel amp all channels are equal. so you need hi rated comps and a low sub, both about the samw wrms level.
this is why people prefre a mono AND a 2channel amp. this way you get more for your money. You could look at some 3 channel amps? they have 2 channels for comps, and then a mono channel which is powerful (higher than just a normal pair of bridged out puts) to run a sub.
although thiese are quite expensive. IIRC Audison do a 3channel at £229