Estat hit on a good point, bi-wiring and bi-amping are two different things. Keep in mind it takes much more power to reproduce bass frequencies than mid to high range. It sounds like you are talking about bi-amping, letting one amp do the bass and the other do the mids/highs, in this case you want the bass amp to be much more powerful. Depending on what you are trying to achieve, it may be easier to get a larger amp. Either scenario involves buying another amp and bi-amping includes more complexity and additional equipment/gadgets.

Either way, as a side note, I have a gfa-5400 for sale. Just email or PM if interested.