Problem Solvers Needed-Got my New XOs installed and am worried....

The only way to upgrade a crossover is to put higher quality parts in place of the old parts using the existing values, if you try to change things bad sound could be the result, as you have found out, lesson leaned i guess.

Assuming the new crossover is broken in, modern capacitors and resistors of the exact same values will change the sound, sometimes significantly. It's possible you're used to your original sound and the new parts aren't to your taste. This may be even More true if the crossover topology has also changed. The single most important factor in choosing audio gear is to know your self, especially the factors that must be there and the negative factors that you can't stand. If you don't know yourself well, changes are a case of throwing darts while squinting.

...now, I'm not brilliant, nor a xover designer, but....

One look at the existing...

https://reverb.com/item/10409571-tannoy-fsm-pro-215-studio-monitors-15-dual-concentric-15-walnut-woo...

...and I'd have replaced all existing components with new and Stopped.😬

If a change Had to be made, iyo....a nice outboard active crossover, bit the belt and bi-amp carefully....

Looking over the charts with the ad above, the existing units seem pretty  'exquisite' for those Tannoys'....even the inductors should be approached with care for a revamp...imho, which that + a buck might get you cross-town on a bus.

Vintage includes components not really made the same as now.  I'd pause at just reconing them, just about that....

They're not speakers anymore....you've got a pair of mistresses...;)
Good luck....both are expensive, as you've discovered....

You forgot the golden rule:  always do a trial of proposed purchases in your own system.  Preferably a long term trial.  Don't buy until you are convinced you like the change.

Amazing how many people read the hype and go out and buy.  One man's meat can often be another's poison.

I sure would like to see a side by side of the two crossovers, (old and new)THAT would tell me a lot.. Any chance you could post a couple of pic in your "details"? If it's lost the highs its a resistor of some type in the HF path.

I'd look where it was hooked to the Highs and see if an inductor or resistor value was added and its GREATER than the original, or as simple as getting the decimal point in the wrong place.

If the HF driver wire was hooked up at the beginning of the HF circuit VS the end of the circuit? That would cause the bass to still be going through the HF side.

A series XO always coming off the + side and on to the next frequency is pretty easy to see the resistance in the path.

Here is the issue I could see in my minds eye. A resistor at the driver that is NOT on the XO. BUT because the resistor was left on or in the HF path the ADDED (but normal) resistor on the new XO doubled the resistance and of course cut the HF signal from getting through.

I would look to see if there is a component that you didn't see or were even looking for. Look at the HF driver terminals and make sure there is nothing in the path and if any type of wiring is going to the Negative side of the driver wire all the way to the new XO.  Just a thought..

If I was the builder though, I would have wondered WHY I had to add the greater value from the old? The light bulb should have gone off.. WHY?
And know a Tannoy XO is not going to be that far off.. IF AT ALL!!

Yet the only customer complaint is "It's Old".  NOT broke.. old...

All I got for no cost. I woke up at 3:30 thinking about that.. And of course it's time to feed the rabbit.. Junior. :-)

Regards