Upgrade from DACMagic? B&W 805S rig

Here is my current system:
B&W 805S Speakers
Cambridge Audio 840a integrated amp
Cambridge Audio DACMagic dac.

Would it be worth it to upgrade from the DACmagic to take full advantage of my speakers? If so, does anyone have any DAC recommendations? I've heard the Benchmark DAC-1 is good. But is it really that much better than the DACMagic? Don't really want to spend over 1500. Right now I think my setup sounds pretty good.
Right now I think my setup sounds pretty good.

My advice - if it ain't broke don't fix it chief. Spend the money on music.
Actually the DACmagic scored higher than the Benchmark in HIFICRITICs test with CD transport, 32 to 22. The V-DAC did even better, 42. I have one and it is very good.
I have tried a million (well 8) DAC's this year, and I ended up with a Bryston BDA-1. You can get one used for about your price.
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Most of the dacs will be a sideways change at best. The idea about a sub is an excellent one. Don't know your listening room so I cannot recommend size. I just went through a sub purchase exercise and picked the Paradigm sub 12 after listening to the Rel B series and the JL. I wouldn't even consider the B and W sub.
source is lossless files from a computer via SPDIF
which computer has a spdif digital output? i thought all they had were optical, usb and some have firewire. do you use converter?

OK, I've listened to the Benchmark and the DACMagic in very good systems but not the same systems and not head-to-head. Still, I did not hear, from either unit, the kind of highs that I would want to live with for a long time.

DACs I have heard which did give me the smooth, clear highs I can enjoy include the Ensemble Dichrono HiDAC, the Audiomat Maestro, the Stellavox ST-2 and the Apogee Mini-DAC. Of these, the Apogee is the cheapest.
What about the PS Audio?
optical = SPDIF. I'm using an M audio transit USB sound card which has an optical out on it.
If you want to really take full advantage for your speakers, make sure they are placed ideally and then add bass traps in all the corners. Better than spending money on subs, so-called upgraded DAC, or even music.
Try room correction. Behringer DEQ2496 or KRK ERGO. These are not subtle differences and unless you run a really nice analog front end make good.