I have a basement room that is 15' x 25' and a budget of $3,000 for speakers + receiver...the kicker is that I am starting with a prewired room and the speaker position lis ess than optimal...ok terrible! Please look at what I am starting with and give me some advise - please help...Matt
Looking at your picture....it does seem less than ideal, but you do have several options.
Is there a central hub where all of these in-wall wires converge, and you are just showing where the wires come out? I'm going to assume that this is the case, but is not part of your diagram. The attached picture shows some rather strange wiring, with the center channel being in the ceiling, while the left/right mains are on the walls. I would extend the center ceiling cable so that you can place the center speaker in line with the mains.
For the rear speakers, there seems to be a center rear and a right rear location in the ceiling, but no left rear. If you wanted to go with in ceiling speakers for the rears, you could re-route the left wall mount up into the ceiling to even it out a little. You could then have a 6.1 system, with the rears being in the ceiling.
If you did not want to go with the in ceiling rears - I would convert the right rear in ceiling to become an in-wall by again extending the cable. You could go with a 5.1 system - with some di-poles on the sides of the couch.
The good news is it is your house - so if you are not happy with something you can change it. I don't think I would go with the mix/match on wall/in ceiling speaker placement with the original picture. The center speaker being in the ceiling several feet in front of the on wall mains would just not work...
I have a father-in-law that has his surround speakers in the ceiling, and his mains/sub as floor standers - and his system works rather well...