I am curious about the external crossovers and if they are commercially available or can be DIYed. Any information you can provide would be helpful.
Cicable was a company that Derek Hughes and Helmut Pullmans started and made some upgraded crossovers for BC-1s, LS3/5as, etc, but they are long gone. The Xtracable crossovers were basically the same and done by Derek for the V2 Stirling LS3/5as, the early ones with the Scanspeak tweeters.
Having looked briefly inside my Cicables and Xtracables they predominantly use Mundorf MCap capacitors and Mundorf Mcoil AirCore copper foil inductors.
The v3.2 crossovers use Jantzen Crosscap capacitors and Air core inductors.
But other than that they are likely to use very similar circuits.
Because the Stirling cabinets use bi-wirable binding posts it would be simple to remove the crossover pub and install it in an external enclosure and then just wire the drivers straight to the binding posts in the ls3/5a cabinet. The main difficulty is building some wooden jigs to make drilling the 4mm holes in the enclosure neat.
RS components make some nice polyester cases which could be used, I have used some of the smaller ones to build my external AB-2 crossovers. You’d just have to find ones big enough, hopefully a little bigger so the air core inductors could be separated a bit more.
Then you could experiment with upgrading the current caps and inductors to the Mundorf ones, I have used the Mundorf MCap Evo Oil ones in the AB-2 crossovers. As the v3.2 crossovers are hand assembled it will be a lot easier to desolder stuff and remove it without damaging the board or anything else.
I might one day have a go at this and if I do will probably put details on the website.

