You might try and find 3 B&W DM303s to have matching speakers all around. The 303 is small enough to mount vertically on a small stand as a center channel.
If you're happy with 5.1, you can probably find a good deal on one of the older Denon or Yamaha recievers here on Audiogon.
If you're happy with 5.1, you can probably find a good deal on one of the older Denon or Yamaha recievers here on Audiogon.