Creek 5350SE or other UK integrated (Arcam, etc.)
The spendors are not very efficient and the Nait is not very powerful, so I can only imagine that the combination will work in a small room, though it would probably work well.
I have a friend in the UK who has a 15 yr old Quad pre/power combination (I think 100w/channel) driving ls3/5s and the Quad's unusual tone controls (tilt/lift) are very useful for giving the bass a bit of a lift on thin recordings. I know tone controls are usually a dirty word, but they can really help the ls3/5s with their limited bass. I've seen used quad pre/power amps for anything from $600 on agon.
Lastly I have a densen B-100, which is similar to the naim, but with more power. I have used spendor3/5 (borrowed from a friend) and it sounded pretty good. The densen is about $1300 new, from audio outlet in NY.
Yes, the 3/5 is VERY inefficient, and thankfully will fill the bottom somewhat with front wall boundary support. Yet I found them so anemic at 84 dB that I bought their big brothers the S3/1p and the great SC3 center channel (an S3 SE with TWO woofers, $700 ea) at 88dB to make a phenomenal, efficient front trio.
I do not know why Spendor doesn't market the SC3 sideways as a Dappolito pair. Sound EXACTLY like S3 SE on steroids.
Sorry to bend the thread, but I just find it more reasonable to use a 6.5" woofer or a second fiver to get +4dB efficiency rather than have to get a huge amp.
That said, I set up an S3 system for a friend with an NAD C541i and an Audio Refinement Complete Integrated with bookshelf (boundary support) mounting, and since he's ok without huge dynamics it works well. His wife poo-poohed the larger S3/1p. Sigh....