I've used a power amp to drive the bass, or bottom binding posts while using the int to drive the top and many times it's worked with excellent results, but a few years ago I used a power amp with identical power ratings at 8 and 4 ohms as the int and the gain was so different that the bass was overdriven causing a very unnatural sound. There was another case where I had 2 different power amps and a pre and I put the amp with double the power rating on the bass and the results were very musical.
Make sure the gain as well as power output is close or you will have an imbalance and unnatural sound.
Make sure the gain as well as power output is close or you will have an imbalance and unnatural sound.