What JL Subs to pair with Harbeth SHL-5 Speakers?

Your room seems to be plenty large enough for the 40.1. As far as total cost and space needs, wouldn't the 40.1 without the subs be a better choice. I use a REL Strata iii sub with my 30.1's, but even then I find integrating the two can be a challenge to get the sub set for every type of music.

Valinar makes a good point that in a your relatively large room, perhaps the 40.1 is the better choice. But if you stick with SLH-5, a pair of JL F113 should be plenty -- provided you split the signal and relieve the SLH-5 of the bass work. If you have spoken to JL Audio, you know they strongly recommend crossing over to relieve the mains of the work that is the sub's specialty. True, integrating subs can be a challenge, but it is doable; and when done right, its terrific. Also, integration is far less difficult when using a cross-over, rather than having the mains rull full range and overlapping the sub in the mid-bass.

Bob reynolds,
Good question. No I would not adjust "level controls for the tweeter and midrange drivers". The crossover is designed for the speaker and best left alone. The speaker has its specific limitations as far as bass extension. I know this is elementary but obviously the subwoofer is only to complement the existing speaker as it is designed. As far as me finding it a challenge to set the sub to accomodate every type of music, I would use a quick example of a couple of different recordings. Beck's new release "Morning Phase" has in my estimation been produced rather bass heavy. That said, I really like the album.There are other albums somewhat similar, such as Robert Plant and Allison Kraus' "Raising Sand". To go from "Morning Phase" to Ralph Vaughn Williams "Fantasia on a Theme by Thomas Tallis", a delightful recording by Academy of St. Martin in the Fields orchestra conducted by Sir Neville Marriner,a bit more of a lower bass boost would be pleasing.
There are times I get sucked into a analytical listening mindset instead of just relaxing and enjoying the music. The Harbeth 40.1 would most probably eliminate the need for a sub. Hence any need to integrate a sub is eliminated as well. Thanks for the question Bob.