ML SL3 adding an active crossover with a sub - HOW ?

I want to bi-amp my SL3's but doing it passively is tough due to mismatched amps

I also have a subwoofer in the system running anything <80Hz due to room issues (long story !)

I am using an Arcam AVR350 as a pre and bass/sub controller driving the SL3's via a Sunfire 300x2 amp (also have a Lyngdorf SDA2175 - thus the mismatch).
The sub is driven wholly by the Arcam.
Using an Arcam AVR feels like a weak link as the on board DAC isn't the best but the bass management outweighs the negative that brings - for now !

I am sold (almost) on the merits of active crossovers and I also hope they may help me get rid of the Arcam in my stereo setup and keep my sub (?)

Question is, how do I do add the active cross over + what do I need to buy ?

PS I am handy with pair of snips and a soldering iron and have some electronic experience so that's not an issue

Any tips very welcome - thanks !!!

You could leave the SL3's stock XO and EQ for the ESL intact and go active xo on only the bass by bypassing (shorting) the inductor and lifting one solder joint (or snipping!) at the electrolytic cap which make up the passive bass xo. Then you will need an RCA 'Y-splitter' to feed the preamp output to a 250Hz (12dB/oct) low pass active (electronic) crossover to place inline before the bass amp and to feed the amp for the ESL, which remains passively crossed over. This is what I'm currently doing on my SL3, and I would encourage everyone to go active xo at least on the bass.

You can look a what I did for my SL3XC project and go full active. But what tosh suggests is very reasonable as well.

thanks Tosh and Jonfo

Tosh, Is the active XO a much bigger benefit in the bass department ?
I was hoping that my panels would be the main beneficiary for new XO as the bass isn't such an issue for me.

Jonfo, thats one epic project - lovely piece of work and lots of interesting learnings on the way

Meantime I have cobbled together a simple passive biamp setup with independent panel/woofer volume controls (keeping my subwoofer linked to woofer volume) that seems to work very well short term and is a nice upgrade as well as flexible in balancing/tweaking the drivers

My current SL3 arrangement (active bass xo and stock passive ESL xo/eq) is one step of a long term upgrade to full DSP xo and eq for both bass and ESL (and not necessarily based around the SL3). Back before December when my SL3 was stock, I used to think the SL3 cabinet itself was adding a 'bark,' 'boom,' or 'overhang' (which got a bit better with more stuffing in the cabinet) which you could also feel on the cabinet walls, and which would also excite parts of the house (windows, cabinet doors, etc). Since going active bass, the bass is so clean, quick, tight, boom-free, and LOW that I would say without doubt, that active xo does for bass what ESL does for highs. Most of the 'overhang' was caused by the series inductor leading the amp to lose control of the woofer. Now the woofer can really perform as designed, it can play ALL the notes, and the cone can even move farther than before without sounding 'wooly.' Cabinet (and house) vibrations are mostly gone. Still thrilled half a year later....

Before I actually bypassed the stock bass xo, I had been deliberating putting in a bypass switch for the passive bass xo, so it could be switched in and out to make quick comparisons between passive and active. But now that I've heard the change, I hope I never have to suffer listening to a passive bass xo again...!

The other benefit of at least bi-amping is that the ESL portion (stock passive xo and eq) can be easily driven by any 20-30W amplifier, as it is the bass section which is power hungry....