Routlaw,
No, I haven't heard both at the same time. I do own a pair of Rhythm Revelators (with external crossovers & .5 dB matched drivers), however, and I'm familiar w/ similar products to the Borealis. I had the same dilemma you did. Here are some of my considerations.
First let me assure you that you can't go wrong either way. One important decision criteria is what size room are you in now? Where do you expect to be in 5 years? How often do you sell equipment? If you are in a small room, the Borealis might be the way to go. I'm in a small room (14 x 16), but don't expect to be for much more than another year.
How loud do you listen? I was using Madisound MDY-4’s, and was tired of not having much bottom end. Moreover, the lack of LF extension strained the midrange at medium listening levels. The Rhythms will do more SPL with greater ease primarily because they won't bottom out so quickly on LF material. I've heard, at length, various Totem products that are similar to the Borealis. The Rhythms do a better job on imaging than the Totems (Model 1's, Forest, etc). With the Rhythms the image is rock solid, fixed in space, and as deep as your mind will allow it to be. Sometimes with the Forests, for instance, the image would tend to float laterally a little bit. Not much to complain about really, but it’s what I heard. I suspect it's due to those extraordinarily tight pre-measured performance specifications found in the NCMS product line (both drivers and crossovers). However, I would suspect that tightly matched Borealis may have a small edge in imaging. I say this because it's always been my experience that smaller enclosures = better imaging.
As far as midrange purity goes, the Scan-Speak 18W/8545 is spectacular. I know, I know, it’s the whole speaker (i.e. crossover, enclosure, cables, etc) that makes the music. I mention the driver because it’s the same in both speakers, and should tend to mitigate any concerns about material discrepancies in purity. I also know you were asking for a direct comparison. That’s one thing I can’t offer. I suspect the Borealis may have an upper hand here, and it all goes back to that smaller enclosure. In my experience, that small enclosure really seams to benefit the midrange. The Totem Model 1’s, for instance, were amongst the best midrange speakers I’d heard.
Of course, every single performance characteristic you mentioned is heavily influenced by the crossover. My advice in this regard is to get the best one you can afford. It makes a very, very audible difference. Short knows his way around a crossover circuit, and he has amongst the best ears in the industry for selecting parts. If he sold his products for $10K assembled (i.e. the “normal” highend way) many would be bragging about them. No matter which one you select, I can promise you that it will be money very well spent.
Last but not least, sorry for being so late with this post. I did a search for NCMS and came across your question. If it’s too late for you, maybe it’ll be helpful for someone else.
Cousindupree
P.S. Unless you’re really good with wood and have a ton of tools, let someone else do the enclosures if you want them to look professional.
