Go Active Crossover or Upgrade existing XOs?

Depending on the number of drivers you have (remember you'll need an amplifier channel for each one) you could look at one of the MiniDSP solutions. If you have three way speakers and are on a budget you could start by replacing the Mid / Bass crossover and leaving the Mid / High intact which would require a DSP with four outputs and four channels of amplification.

Please remember 85% of Xovers in speakers unless very $$
are substandard.i have been modding Xovers and internal electronics for over 25 years. The Xover parts usually at best have solen capacitors or the China specials Keven speakers at $10 k +
shocking but true I had a 15k Martin logan ,and Sonus Faber 
both had the lower quality white mundorf evo caps.
in your Tannoy he Jupiter copper foil would be excellent 
and use the worlds best resistors from path audio.for my audio get together I demonstrated a experiment a stock monitor audio studio speaker, and one I added $1000 in Xover parts upgrade
it went from a $1500 to a $5k speaker in sound quality vs several 
well known speakers . The Xover is the brain,or heart of all speakers, also buy good WBT Copper connectors not the junk 
gold over brass which comes with most speakers .brass is horrible in natural fidelity vs Copper and has 4 x the resistance = distortion 
i spent literally 1,000s of hours listening and comparing .i usually also replace the cheap internal wire as well as jantzen a Copper inductors . When using a electronics active Xover you can tune it but it looses the flavor of the great capacitors which adds that depth and live presence Lon paper a active is more ruler accurate 
thst applies to solid state vs vacuum tubes in accuracy but 
having a vacuum tube in the circuit adds another dimension in realism. Your ear is the final word in tonal accuracy thst is whst I rely on more then just measuring equipment ,which is just a guide or starting point. After 40 years in Audio and having owned a Audio store .i have had pretty much most things out there learned from many excellent techs on modding .that is why modding 
gives back so much more per $$ dollar spent in fidelity vs just buying new ,for rule of thumb  25% or less  of the product cost actually goes into the parts ,the rest overhead,R&D,and overhead!!

I think mijostyn1 and barts28 made salient points.  Audio Research sold both active and passive crossovers early on when they had a co-marketing agreement with Magnepan.  (Some may be interested in learning that Diller was with Johnson at AR way before he went over to Winey's company.)

The passives were available in a few varieties and the actives, which sell for TONS of money today, were also either 2 or 3 and came in several varieties.  Back then, Magnepan wanted you to tri-amp the speakers and Audio Research wanted to sell you many amps, so we sold and set up these systems for customers.

As I remember, and it was 40+ years ago, so take this with a grain, the actives were easier to set to the room than the passives, but both worked rather well when set up properly--most good equipment does.

As to which is better, I would (if I were doing this today) probably go active and put as many amps as possible (barts28) in the system.  If you have Maggies, they eat power, so more is always merrier if you like to crank up Mahler or Zeppelin or whatever.

Cheers,

Richard

@audioman58 from your post would you recommend the Jantzen audio inductors or if not which? I was under the impression their foil inductors were very good but again you've been an expert in this area I rather have your opinion