I have a pair of B&W Matrix 803 S2's from about 20 years ago. Would they benefit from replacing both the HF and the LF crossovers of just capacitors?
I had all the Caps changed in the x-overs of a 30 year old set of speakers - replaced them with Mundorf caps.

Cost $250 for both x-overs

As long as the speaker surrounds are in good shape you won't be wasting your money - I had to have my speaker surrounds replaced also.

They now sound much better than they did with the original caps

I can highly recommend Mundorf :-)

Steve - I just remembered I also had to have a couple of the heavy duty resistors replaced - they were looking "well worn" - but they we're cheap compared to the caps.

Steve - also take the opportunity to assess the state of the internal wires.

Copper Quality has come a long way since they were built and it may be advantageous to rewire them as well, but don't go overboard with really heavy gauge wire.

Something like Furutech FS 303 should suffice, but separate the two conductors.

For the short runs in the speaker enclosure, cable gauge is less important but copper quality should reap benefits.

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Mental - I was just really fortunate to find a technician that is focused on value and service and not on his wallet :-)

The first job he did for me was to rework my tube amp - gave me two upgrade options and recommended I opt for the cheaper of the two - strange but true.

Most places don't have the required skills to make those kinds of calls

Needless to say - He is never looking for work :-)
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Mental - since you are into DIY you might want to checkout these PC's and IC's

Cable Construction

The power cables are very dynamic, contribute greatly to a much better image and allow the amp to exert much better control over the speakers - they are also very quiet

I have them on every component

Scroll down to view the IC's

For the IC's I use 24 awg solid silver wire for the signal wire and KLEI Absolute Harmony for the RCA's

They are very detailed, open, neutral, dynamic and spacious (great image)

You can use other RCA's, but I've found the KLEI RCA's work the best

They are not quite as good as the KLEI gZero20 IC's that I run on my analogue rig, but I do use them on the digital side and they will get you closer than most of the store bought competition

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Mental - I also found the dh-labs to be an excellent toslink. I have three on
different components and they are very clean and crisp :-)

That was after trying Chord and Van den Hul products - they paled by

If you are going to look at the KLEI Harmony RCA range - start with the Silver
Harmony for analogue IC's.

The Copper Harmony are very good for digital IC's - I've tried them with the
spiral architecture and they worked better than my purpose built 75 ohm

They do work very well for analogue, but the Silver Harmony and up are much
better at analogue.

The nice thing is - on the right cables you actually hear the improvements
quite clearly from one model to the next - at least on my system.
- crisper dynamics
- wider/deeper image
- deeper bass with more control/texture
- extended top end with more clarity

They should sound really nice on the Krell/Oppo combo