Raz,
You've got some tough choices to make. Let me run down the situation;
First lets look at the foundation of your system; the amplifier. I tend to give Rotel the nod for home theater, while I give Arcam the nod when it comes to music. Here's what I would do in your position; determine how loud you want to take things. If you like to crank the volume a bit, the Rotel receiver will be the more ideal match. If you do not intend on cranking the tunes and music to extreme levels, I'd suggest the Arcam simply for audible step up in harmonic richness. Either receiver should deliver rock solid performance and power either the Sapphire XL or the Beemers well.
Now onto the center channel; It's already been said... get one. Building a dedicated dual purpose system with a receiver at the helm _without_ a center channel is like trying to play baseball without a mit. VCR aside, while there are still DVD's that come mixed for two channel listening as well as multi-channel - most anymore are mixed with information specifically for the center. You will be literally missing critical information without one.
And now finally, the Beemer 704's versus the Sapphire XL's; This is a tough call. On one hand, the 704's are a very attractive tower that requires no additional expense of a stand. Their metal dome tweeter will be more "alive" and forward compared to the soft dome on the Sapphire XL, which is a bit more laid back. This means the detail of a movie (or even piece of music) will be more easily discernible. B&W's have a long and distinguished history in audio and sport a nice open and detailed sound that many have come to love. While I feel this speaker lacks a bit of luster when it comes to rock/electronica/r&b/ - I find it to be pretty spiffy with jazz and small-scale classical. Movies wise, it's not the kind of speaker to thump you in the chest ; however, its semi-aggressive presentation will bring out all those movie thrills and bullet zings that'll keep you gripping your chair.
The ACI Sapphire XL's will require a stand. While their high end is smooth, the mid-range is less colored and oozes out great tone. Oh yeah, the bass from that small speaker ain't too shabby. With room gain, you can get strong output down into the upper 30hz range. When it comes to music; I'd give the nod to the XL. It is a more versatile speaker that can handle virtually any genre with aplomb. They are also far less fatiguing (over extended listening sessions) than the Beemers. I also feel that the Sapphire's just have a bit more 'soul'. For theater, its a toss up. My bias hides within what a speaker can do for music, not movies. I will say this though, if I want something a bit more thrilling and exciting - I'd chose the 704's for movies. If I wanted something non-fatiguing that I could settle down with for the long-term, I'd go XL's. If I remember correctly, Mike has a few specials going on with the XL's - so theres a chance you may be able to get a better price than whats on the website.
Good luck !
