Upgrade amp. or speakers first?


I have a Krell KAV 300i, and a pair of B&W N804's, all about 12 years old. Want to upgrade and want to know which should be first to go. The speakers or the amp? I listen to mostly jazz, some small scale classical, and R&B. I am leaning towards the 803D's or 804D's. Will budget up to 8k for amplifier(s). I have listened to some McIntosh, the new ARC integrated and Rotel amps. I recently got an Ayre QB-9 for digital source ( ITunes-Macbook ). Will upgrade, but not all at once. Thanks for any suggestions.
atj2
Post removed 
I'm listening to everyone's suggestions and appreciate your input. I thought I would upgrade the weakest link in my system and from what I can tell, the weakest componet is the Krell KAV 300i. I may keep the N804's for awhile longer. My system ( with Ayre QB-9 ) sounds at least as good as some other ( 804D's without QB-9) systems using McIntosh or Rotel amps. So I thought if it sounds good now, if I upgrade the amp., to Pass, ARC, the new MD-309, integrated or possibly some of the pre/power comb's., I would get even better results. Even though I like the B&W sound, perhaps I should listen to some other speakers
( $7K- $10K).
I attended RMAF this year and made a point to stop into a room that I had really enjoyed last year. The only thing that changed significantly was the speaker. A different make and model was chosen this year. The amplification remained the same. This room year was a disappointment.

What's the point? Well, in my opinion, the speaker selection changed the sound significantly, which affirms why I suggest selecting speakers first, and then selecting amplification that will drive them well.

Obviously, if you own or are considering buying tubed amplification...and any of the sub sets of tube amplification, you must be careful to select speakers that can be driven by the amplification that you own or that's on your radar.

That said, there's no right answer, and there are several roads that will get you to your destination.

Good luck.
10-27-10: Tvad
This room year was a disappointment.
Very sorry for the lazy editing.

Should read..."The room this year was a disappointment".
For sure you can change speakers and the sound will always change dramatically but is it change you can live with? Been there done that. Sure for a different sound get a different pair of speakers.

The single ended guys go at it the other way, They start with the amps and then of course choose speakers to go with the usually limited power they have.

From my experience a superb sounding amplifier will sound superb or at least very good on a set of capable speakers.