Loudspeaker for second system

Before I opened your post I was already thinking "ELAC". All the reviews I have read have been positive. I haven't heard them, but do own the Pioneer 22s for another system in the house that sound amazing for their price of $130/pair. Andrew Jones was the engineer for those. I have no doubt the ELACs sound every bit as good as the reviewers say they do.

Tons of options. Are you looking new or used? 

The Elac B6's are phenomenal. There's also a pair of ASW 110's available on Agon now that would completely satisfy you. 

Be careful with Elac.  They need very good electronics to sound good.  They can be a good value, but personally, many of their models aren't 'great value' speakers as everyone says they are.   They can be very bright and fatiguing.  Now days many equate that to 'great extension and bigger soundstage'.   NAD is a good match for them.  

If you can, you also should look for a pair of Vandersteen 1's or even a used pair of 2's (late model) as they are outstanding values at listed price let alone a good used set if you can find them.  The 1's, to me as well as many reviewers, have become one of the best values in floor standing speaker.

Doug, I have heard their line for years now.  Like many other lines out there, you don't always get better quality by moving up.  Often times they have a totally different design as you go up and it's not always better.  Often times budget companies do a nice job for the price points, but once they step out of that realm, they lose their value.  Happens very often I feel.