i auditioned the ls17 ad ls26 side by side, same system :
wilson w/p #8; arc ref110, k5xe , transparent ultra mm cable + transparent intercons. room accoustics - somewhat damped [not my livingroom]
the ls17 performed nicely overall, but there was no compariso with the ls26. i found the differences somewhat substantial compared to the ls17, perhaps more so than davemitchell suggested . going with the ls17 is a big compromise, if you have very revealing speakers.
one thing i have learned in the last few months of itense equipment auditioning: , if other parts of your system arent up to a similar levels of sound reproduction, and you dont plan to upgrade the weakest links in the chain, then the differences afforded by the ls26 may not amount to much by the time the music comes thru the speakers ! it's as much an issue of real world budget as listening aims. that said, the ls26 was significantly better than the ls17 in my evolving system.
other: i listen to mostly classical music, much of it chamber music. conservatory trained. nuance is critical to me.
cheers.