Helps me with long term system development.

If you like your speakers, then I would keep them. B&W are nice speakers.
In my opinion, I would upgrade the preamp, then amp, first.

Hi Jbuhl - 

I have some experience with some of your setup and here are some thoughts.  First of all let's talk about your speakers.  I randomly picked up a pair of DM604s several years ago for only $250 on Craigslist and was really blown away by their performance especially considering what I paid for them.  When I owned them, they were powered with a Class D 500 WPC amp and they sounded great.  The reason that I bring them up is that I actually preferred them over the 684s that you have.

I've since moved up the B&W range and have tried most of them.

In my opinion, the biggest bang for the buck in the entire product range and within your budget is the seldom discussed Nautilus 703.  Probably not their prettiest speaker but man they absolutely sound fantastic for what they cost.  I seem to recall having picked up the pair that I had for around $800 (which was a good deal) about 6 years ago.  They are a definite upgrade from where you are now.

As far as amplification goes, I would stick with what you have for the time being and swap out the speakers first and then decide if you need to go a different direction with your amp - it's usually better to swap out components one at a time, assess the change, and then move forward rather than trying to change too much at the same time.

Given your choice of B&W speakers and Class D, I would not recommend the Sumiko cartridge on your list.  On paper it looks like a good deal (HOMC that will pair with your existing MM preamp input) but doubt that you'd be happy with it.

I've had a couple of Blue Point #2s and find them to be fairly detailed, but also a bit thin, dry and not very involving.  For just about more and with the Sumiko range, the Blue Point Special Evo III is in a completely different league - sounds much better.  For your phono preamp input, anything around 2.5-4mv will work fine.  In a similar price range as the Sumiko you mentioned, the Ortofon 2M Blue is actually a much better sounding cartridge than the BP2 in my opinion.  I'm sure that there are plenty of MM and HOMC options that you'd find preferable to the BP2.

Greg

Put Vandersteen on your list for speakers! A FET solid state amp would go nice with the Rogue tube preamp!
http://vandersteen.com/products/model-1ci
http://www.avahifi.com/products/power-amplifiers/synergy-amplifiers

As a Vandy fanboy, I would second donvito's recommendation, but I want to respect jbhul's current speaker before making any future updates speaker-wise.
B