You could buy 2 more of the nxg speakers and install them in the wall. As it stands it looks like you are going to have an annoying situation due to one side of the TV having a countertop and the other not. So its like 2 book shelfs with 1 stand or something.
Also you can get the polk monitor series at newegg for way less than the TSI series and they are esentially the same. For instance the monitor 40s are just $120. However I do not know if they will match your center channel. It is so weird that they took the time to install the center channel in the wall but not the front left and right. Even if I was not going to use the in wall speakers I would probably install them just for the resale value of the house and before they stop making the same model.
Also you can try pauls TV inside art van, they had the 1612 for $100 when i was in there, it was the display model.
Different recievers have all different pros and cons but in your price range you are going to have to go with which ever one is on sale. Another option would be to skip the sub and put more into the fronts / receiver.