Best subwoofer to pair with Vandersteen Treo CTs??

I looked up the compatibility for 2ces once on the REL site. It was the S/510s if i recall. 

You can go to the REL site and put in the parameters to see which sub is right for the Treo. My input for your system yielded the S/812. 

https://rel.net/blog/speaker/treo-ct/?intended_use=music&room_size=medium

I have 2ces and Vandersteen 2wq subs with high-pass crossovers between amp and the 2ces. I haven't heard better bass in the 20-40k system range, but I am biased. 

2ces and 2wqs, sealed-box enclosures.

Treo CTs and REL S510s, ported and passive radiator respectively. 

Vandersteen 2wq or Sub 3 is ClassA/B amplification

REL is Class D. 

Finally, Vandersteen subs can be ordered to match the finish of your Treo. 

Good luck! 

Paul.

I'd go with the Vandersteen subs for a few reasons. One they are probably voiced to match Vandersteen main speakers so they'll blend better with much less color differences. Second they include the 11 band Vandersteen bass controls which will allow easier solutions to room problems, a major factor in bass response. Finally they include a high pass filter which the RELs and other subs don't. This reduces the main speaker bottom driver extension increasing power handling and also improving the openness and clarity of the main speaker bottom driver.  And fourth the Vandersteen loading is closed box which has superior bass quality to ported or passive radiator loading. For all these reasons logically this is a no brainer choice. But as always it's still always best to have a real audition before buying or the right of trade back if they aren't what you are looking for.  

@aphilc Have you joined and/or read comments on the Vandersteen Owners Forum? Plenty of friendlies there with direct experience. Cheers,

Spencer

Thank you all for your comments. Will probably pull the trigger on the Vandersteen Three’’s.