Best amplification for Magico S3 newer version on your experience

FWIW I’ll give you my experience for driving a pair of Magico S5’s. I started out using a Luxman m900u. I thought it sounded great. Then I switched to a Coda S5.5 amp as I’d had the Luxman for a long time and had the itch to change to something new. The little Coda outperformed the Luxman in every way. The Coda is only 50 watts class A into 8 ohms and doubles to 100 watts at 4 ohms and can drive a 2 ohm load at 200 watts. I think the key to its ability to out perform the Luxman is that it draws 100 amperes which a lot more than the Luxman even though the Luxman is 150 watts into 8 ohms and 300 watts into 4 ohms. The little Codo retails for $6,400. I recently saw a used one for sale on either this site or usaudiomart.  That’s just my experience. Good luck!

I've never heard the S3s, but the CAT amps sounded amazing on the S5 MkII

The S3s are a difficult load. For a relatively cheap amp I'd try the Schiit Tyr mono blocks. They have a huge power supply for the money using chokes(which produce super smooth current) needed for the large current draw for the S3 load. Power supply cost money and doesn't show up in specs. One of the things you get in costly amps is huge power supply because they can afford it. But even six figure amps don't use chokes and perhaps they should.

@OP. In my experience, the 509 does not sound as powerful as its rated specification suggests. You could try a Pass Int 250 for comparative purposes. If nothing else, it will demonstrate that not all competently designed amplifiers sound the same.

Depending on your budget I agee Coda makes very good underappreciated amps. They fly below the radar. Your room isn't that big  too but  high amperage they put out is rather robust. That helps with the lower listening levels. A #16 would be magnificent. (I too have the s5.5 and it is amazing) Good luck making those Magico's sing.