I am yet another victim of a low WAF. Not only do I have to get bookshelf speakers, but I don't have a lot of vertical space available. I am very partial to PSB's, and was wondering if there is any reason I can't use two Image 9C's as fronts with an 8C. I welcome any opinions, and this money is burning a hole in my pocket.
I don't know about the PSB's but the B&W LCR600 series 3 or LCR60 series3 might be worth considering as they are designed for vertical or horizontal placement as well as for use as either center, main, or surround speakers.
Vertical placement is usually better because it doesn't cause comb-filter problems with a d'appolito speaker. If you have to place your speakers horizontally it would be best to get three identical 2-way bookshelf speakers and put them laying on their sides. But if you still go with three centers I suggest you take three identical speakers and not a smaller center, this way the front soundfield will be as uniform as it can.