Affordable Audio's May 2010 issue has a review of Polk SDA CRS+ Speakers, by Jake Montzingo (see pp. 32-34).

I especially liked reading Jake's comments about how he enjoyed the CRS+ speakers post-tweeter / crossover / binding post / interconnect upgrades:
The Redux
A few of you may have figured out by now from the pictures that my pair of CRS+ do not look quiet stock; and in fact they are not. Being that this particular pair of speakers is twenty years old, I felt that they needed a little refurbishing; and luckily so did Polk! A few years back, Polk decided to release a pair of replacement silk dome tweeters for their vintage Monitor, RTA, and SDA lines, named the RDO. This tweeter was not only a direct replacement for a no longer manufactured tweeter, but was also a modern upgrade in looks, technology, and sound quality.

As soon as I discovered this authorized tweeter replacement, I placed my order for these silk dome fantasies. At the same time, I decided to upgrade the crossovers with new components consisting of Sonicap capacitors and Mills resistors, as well as install new binding posts from Dayton Audio and built a custom SDA interconnect using 12g wire. After all the work was complete and the speakers had received 150 hours of break in using mixed classical music, I was nervous to find out exactly what new creature I had created. In my lab coat and welding goggles, I threw the over sized electrical switch as my hunched-back accomplice cackled in the background. The sound that flowed out of these newly modified speakers was much better than before, and frankly, better than it should be. Having come to know the sonic signature of the speakers before they were modified, my ears would not believe that what I was hearing was similar to the original sound, only much improved! The silk dome tweeter really tamed the high end and smoothed it out. The new capacitors and resistors not only improved sound quality, but tightened up imaging even more and heightened dynamics. Itís alive!
Seems that a number of posters in these forums have come to the same conclusions about how Polk SDA speakers, after many years of service, still respond so well to some enhancements.