I think you can get a line/powerlink adapter that would work with the 7-series.  All of the 7-1/7-2/7-6 have the same power rating so I don't know if they are appreciably different.  For a 52" TV the 7-2 would be the best choice, I have one mounted under my sharp 52" aquous and it is nearly the same width.  The 7-6 is freaking huge.  I have also a Samsung 55" LED mounted right on the wall like a picture.  The 7-series would look strange wall mounted below this as they are quite deep compared to the TV.  Because of this I opted to go with two BL3's on mini stands.  I would just ask the wife what she likes best.

I have the Beolab 10 triangular center channel speaker and am extremely pleased with it. You can wall mount it beneath the tv and it is quite slim in depth. Also, the front grill is VERY easy to remove to replace with any of the color options. However, the replacement grills are quite expensive.

BTW, my Beolab 10 replaced a pair of Beolab 4000 speakers that I had been using for the center channel. I felt that the Beolab 4000 speakers were quite poor in performing as a center channel. They just couldn't keep up with the Beolab 8000 speakers I had for front right and left speakers. The Beolab 10 does a MUCH better job. Also, the Beolab 10 has an acoustic lens.

A 6000 speaker will not feel properly balance due to the placement of the woofer and tweeter. 

I agree with beojeff, don't get a BL6000 for a center.  That will sound strange and off balance.

Thank you both for your input.  If I can find a single BeoLab 3 or a BeoLab 10, I think I'll go with one of those.