Have you been able to listen to some other systems? If so, did they sound too dark (i.e. not bright enough) to you? If that is the case, then maybe it is just what you're used to. But if you think your setup sounds darker, then perhaps not. Either way, you're entitled to have your preferences - every single system makes compromises. Just because you prefer to compromise one thing rather than the other doesn't make it wrong.

The cheapest experiment is placement - try moving them further away from the wall first, and otherwise move them (and you) around.

How does the setup sound through headphones? If it is satisfactory (bright enough), then it may be the speakers. The speakers are the mostly likely candidate anyway, and B&W aren't known for being bright from what I understand. But try placement - a BUNCH - first.

If the 'phones sound comparably dark, the next candidate is the phono stage, then the cart in terms of likelihood.

On the other hand, you may just decide you prefer it this way. Oh, the joys of hi fidelity...

Just so you know audiophiles use the term "bright" as an insult or a criticism for when there is too much treble in a product. With that in mind most studio monitors that I've heard are BRIGHT. If you are used to studio monitors (and the associated electronics) those are significantly brighter than most home gear. I liken it to cheap red wines that may be sweeter than high quality wines. An experienced wine connoisseur would find them sickly sweet. Don't bother asking yourself which one sounds "better" because that's such a subjective question it will only drive you mad. Instead ask yourself which sounds more like ACOUSTIC instruments in REAL space. Many times the gear that sounds "better" than real life after extended listening will cause you to quickly tire of listening whereas, all things being equal a good hi-fi system will allow you to listen and enjoy for longer periods of time.

Room position can make a HUGE difference. Also there is no mention of cables and power conditioning? What are you using in those areas? Both have a big impact on high frequency extension and detail

I've heard almost every level of Monster cable and they all are very, very colored. Interestingly enough these colorations aren't consistent. They seem to be specifically tailored them to the way they think someone's system would sound that is buying a particular level of cable. I haven't listened to Acoustic Research's cable since college (which is almost a decade ago) but they really sucked back then. If you have a good relationship with a local dealer talk to him about the specifics of your system and your goals and ask him to loan you some cable that he would think are appropriate. I'm pretty cynical when it comes to cables. Don't take that to mean that I don't hear a difference. Take that to mean that I hear too much difference. I believe that most cable manufacturers are INTENTIONALLY coloring the sound of their cables in an attempt to grab market share and to be different from each other. Essentially, many of them are making passive equalizers with permanent settings. In the long run that isn't what you want. A good way to test for this is to take the cables and listen to them NOT ONLY in your system, but in a super resolving system (possibly at the dealer.) The second step will reveal difference and sonic issues that your system might miss. I'd recommend Audioquest cables, if you don't have a local dealer they are easily available through internet dealers.

It should also be mentioned that audio equipment takes time to break in, especially new products. Don't judge a system before everything has at least 150 hours. A good way to speed things up is to either let a CD(on repeat) or a FM tuner play all day at a moderate level while away from home. Preferably Classical because of the increased frequency response and dynamic range. Cable also take time to break in incidentally so when borrowing some see if the dealer will lend out some that he uses around the store while the store is closed for the weekend.