High value, giant killer speakers?

Well, it really is the combination of speaker, everything upstream and the room size/setup. Too many variables, hence the 9,359 suggestions here.
For what it’s worth I just bought a pair of Elac Uni-Fi UB5’s for my brother-in-law along with a new Parasound A23 amp, a used Para P5 pre-amp and a new pair of Polk Audio PSW505 subs (the P5 has dual sub outs with variable crossover). As a system they work quite well. It took some time to dial it in but it sounds quite impressive even without coming room treatment. He has an older Sony Blu-ray player as a CD source. It will improve over time but it is orders of magnitude better sound than he has EVER had before! The small Elacs are a good place to start.

I have Tekton Design OB Sigma hybrid open baffle speakers, Hsu Research 10" subs driven by both a vintage Ad Com 555II and Parasound A23’s in bridged mode driving the passive subs. I believe Tekton Design is another good value place to start in speakers. Andrew Jones (Elac) and Eric Alexander (Tekton) are doing very nice design work!

Actually  douglas_schroeder has a point.
Sometimes its more important to know what NOT to buy, than what to buy.
 How about starting a post about what speakers to stay away from?

I wanted to add that I recently purchased a used pair of Dynaudio 42's, and to me they sound pretty similiar (from what I remember) to the original cbm-170. I'd say the Ascend has less bass, a brighter tweeter and a more detailed midrange. The 42 in comparison has a thicker, darker midrange, more bass slam and a much better tweeter. Overall they are both ruthlessly revealing and sound fantastic with certain music, but too harsh on other music. Both are much differen't than a forgiving speaker like a psb.

I have been comparing Maggie LRS with Zu Dirty Weekend - powered by Schiit Vidar monoblocks and a Freya preamp. 

The Zu's are very good with a sweet sound and beautifully-made cabinets from Utah.  They also let me go a little past their 60-day full-refund period while I waited on Magnepan LRS's to arrive. 

The music started out of the LRS's before I even sat down and I knew I was listening to something more profound.  I listened to Mahler's 2nd and was even moved to tears in the 4th movement.  That totally surprised me and pretty much made my decision. 

And the usual caveat:  this is true for me and my partially damaged ears in my particular listening room.   I think the LRSs'bass is somewhat muddy on genres with a driving/thumping bass lines, so eventually I will find a subwoofer to fill out the LRS's.  But surprisingly, I really liked the way the LRS's handled bass on jazz trio and vocal music.  The Zu's do a very decent job from high to low.
Brian