I'm not going to touch on how ridiculous the concept of 9.1 is, but I will say that if your receiver doesn't have the proper internal amplification for a true 9.1 setup, then you should not setup your home theater as 9.1 at all and should stick with 7.1 as your system is designed for.

Adding additional front speakers which are not placed and designed specifically to work together can harm the audio, not make it better.

Generally speaking, the best way to get better sound in a room is by properly treating the room acoustically so that the environment is actually better for audio.

People do all sorts of unorthodox things, yet they rarely know when things actually sound better or not. Adding unmatched speakers may give you more punch at certain frequencies, while at the same time cancelling other frequencies which are supposed to be there.

9.1 is a new way to get people to spend money, yet actually having a room which just sounds good with 5.1 is VERY difficult to accomplish for most people and instead of learning about sonics and how to make the room itself sound proper and accurate, most people will just glom onto the latest technology as if it will help things to sound better... Often when they don't hear enough audio from those speakers, they artificially inflate the audio for an even more unrealistic environment.

I would simplify and shoot for accuracy instead of looking for a neat trick.