B&W 801 Series 2 - vs - KEF Reference 203/B&W N805

My dream speakers are Nautilus 801's or 802's but the price point is still higher than I can justify.

I have and love KEF Reference 203.1's in my main setup, and Nautilus 805's with a sub in my second setup.

How would the much older, yet esteemed 801 series 2's compare to either of my setups, using good amps and sources?

I listen to everything - Classical, Rock, Jazz, Blues, Electronic, Alternative, etc.
N805 with sub will still give you better bass definition and details vs. N801 which may dissapoint you.
Do you mean those gigantic, aging, hard to drive beasts, Matrix 801's? I won't make any more comments since that is unclear, to me at least.
If Nautilus 801 (or 800) are your dream sprs, you would probably find the old 801s ("matrix" IIRC!) insufficient. By comparison they are "sweet", with a rounded top range, blown out/ beefy mid-bass & insufficient lower bass. Romantic sound! They are also very difficult to drive well. But whenever you play 1812 or Symphonie Fantastique etc on them they have this impressive "dynamic" effect ... i.e. they go "boom" nicely:)

As suggested above the 805s + sub do a better reproduction job (i.e. more extended, if somewhat tricky to integrate well).
BTW, are you sure they are better than yr KEF Reference 203.1? I don't think so, but I haven't lived with your speakers.
IMHO 801's have is 'bottom flagship' of all speakers for price vs. performance(burp).