What can I do to treat my room acoustically?

I just moved into new house. My speakers now sit in a niche about 10 feet wide with 9 foot ceilings and the niche is about 3 feed deep on one side and 2 feet on the other. My beloved system doesn't sound good. I need some pro help.
First thing. I don't like the 'sound' of your speakers sitting in a niche.(pun intended) It already sounds congested. (no pun intended)

With the house totally quiet, stand against the back wall inside the niche. Walk quietly and very slowly away from the wall and further into the room while speaking in a normal tone and volume. When the sound of your voice changes in tone; becomes thinner in texture, your voice is no longer loading with the rear wall. Locate as near as possible the point of change and mark it with masking tape. Extend the tapping parallel to the rear wall ( you'll need to average your uneven dimension here). The tape line should be the starting
point for locating the front loudspeaker baffle. I would run one side of your stereo at a time moving the loudspeaker slowly inside and outside your tapped line, carefully listening for bass to increase or decrease and also for nasty bass nodes where a particular note is considerably louder than the rest and sustains longer as well. Do each side separately and then run the system in stereo. Spend some time listening all over the room and not just in the new sweet-spot. There will always be a trade-off between mid range clarity and
deeper, more powerful bass so you can actually tune your preferred sound with small speaker placement adjustments. The front baffle should always be near the tapped line, normally within 6-8 inches of the tape. Distance between the loudspeakers and their respective distances from side walls is another two man job and possibly another day of listening-adjustment-listening......
There is a specific place in the room for each of your speakers that is optimum and irregular rooms do not always comply with formulas and golden rules. They are not a bad place to start.

This is getting long and to perform what I have described above really requires two focused individuals in a quiet house with lots of time and patience. Or you can hire someone like myself who has years of experience with this task.

Bottom line here is to get the speakers out of the niche, even if it is just out. Performing this task will be a revelation. I wouldn't even begin any room treatments until your loudspeakers have found their natural home.