How do the Elac Uni-Fi UB5s compare to more expensive bookshelf speakers?

I had a chance to hear Both UB5 and LS50 twice. The first time the LS50 was paired with a Primaluna integrated and it sounded incredible. I simply could not believe what was coming out of these little box speakers. I had a similar reaction when I heard the UB5 paired with a $400 NAD integrated. A $3500 system vs. an $800 one, both impressive but for different reasons. No question the PL/KEF combo was in a different league.The second time I heard the LS50 I asked the sales guy to switch the amp and hook it up to the same NAD integrated I had heard paired with the Elacs. Even though this was not an A/B test - the dealer did not carry Elacs, I thought the Elacs sounded better - much better bass, detail, etc., with the lesser amp. I just wished I could hear the Elacs with Primaluna amp but I can only imagine how much better they would have sounded. Bottom line (for me) was if I were to buy the KEF, I would either have to be prepared to buy a high quality amplifier, otherwise I'd just go with the Elacs and buy a comparably priced amp. This is all if the SQ is the only criteria otherwise LS50 is in a completely different class when it comes to the build quality.

Another point to keep in mind is the cost of the stands. They tend to make a noticeable difference in the sonics so you don't want to skimp when buying a $1500 speakers.